Condensed Matter Retreat 2026 @ BBB Baden

11 Nov 2026, 08:00 → 12 Nov 2026, 23:30 Europe/Zurich

Aula Martinsberg (BBB Berufsfachschule Baden)

Colonna, Nicola (PSI - Paul Scherrer Institut), Gerber, Simon (PSI - Paul Scherrer Institut), Mazzone, Daniel Gabriel (PSI - Paul Scherrer Institut), Normand, Bruce George Alexander (PSI - Paul Scherrer Institut), Salman, Zaher (PSI - Paul Scherrer Institut), Shepelin, Nikita (PSI - Paul Scherrer Institut), Staub, Urs (PSI - Paul Scherrer Institut)

PSI Condensed Matter Retreat 2026

The PSI Condensed Matter Retreat brings together early-career and senior scientists working in condensed matter research at PSI. The event aims to promote scientific exchange, encourage networking across laboratories and techniques, and strengthen connections between researchers using neutrons, muons, photons, and complementary methods, as well as theory.

The retreat is aimed primarily, but not exclusively, at researchers from CNM, CSD and CPS. PhD students, postdocs, and junior scientists are especially encouraged to present their work.

This year’s retreat will remain open to all areas of condensed matter research at PSI. Topics include quantum materials, magnetism, superconductivity, topology, ferroics, driven systems, advanced materials and techniques, materials under extreme conditions, and new ideas for future research.

The programme will include regular talks, posters, flash talks, overview talks, and an invited plenary lecture.

The registration fee for this 2-day event is CHF 80.00 per person (includes coffee breaks, lunches and the apéro riche on the first evening).

Wednesday 11 November

08:30 → 09:00 Welcome & Registration @ Aula Foyer

09:00 → 09:10 Welcome to CMR 2019

09:10 → 10:10 Facility/infrastructure talks: Session 1

Convener: Piamonteze, Cinthia (PSI - Paul Scherrer Institut)

09:10 Update from SINQ

SINQ provides a versatile platform for neutron science, from quantum materials to industrial applications. This talk reviews recent developments in instrumentation, digital workflows and source renewal, highlighting how they address ageing infrastructure while opening new experimental possibilities. Examples include Amor and WARP, the Digital Lab, and the proposed UFO irradiation facility. Looking ahead, SINQ++ connects these developments within a broader vision for new scientific capabilities, stronger links across PSI and the Swiss research community, and sustained international partnerships, thus turning today’s challenges into opportunities for SINQ’s future.

Speaker: White, Jonathan (PSI - Paul Scherrer Institut)

09:25 The Swiss Muon Source SμS

The Swiss Muon Source SμS is one of the leading international user facilities for
muon spectroscopy research. Six permanently installed instruments for muon spin
spectroscopy (μSR) and one non-permanent instrument for Muon-Induced-X-ray-Emission
(MIXE) are available. The μSR program typically uses positive muons as highly sensitive local
magnetic probes to study a broad range of research topics in solid-state physics, chemistry,
materials science, semiconductor, and energy research. MIXE uses negative muons, which
are captured by the target atoms after implantation, emitting an element-specific cascade of
X-ray radiation, which allows non-destructive elemental analysis to be carried out on tunable
depths from 0.001 cm to > 1 cm. In this talk, we will provide an overview of the facility and discuss
future prospects within the IMPACT/HIMB project and the newly established NCCR Muoniverse.

Speaker: Prokscha, Thomas (PSI - Paul Scherrer Institut)

09:40 SLS

Speaker: Willmott, Philip (PSI - Paul Scherrer Institut)

20261111_condMatRetreat.pdf

20261111_condMatRetreat.pptx

09:55 Lib4Ri

Speaker: Bachmann, Michael (Eawag)

10:10 → 10:40 Coffee Break @ Aula Foyer

10:40 → 11:20 Contributed talks: Session 1

Convener: Müller, Markus (PSI - Paul Scherrer Institut)

10:40 Studying altermagnetism with muon-spin spectroscopy

Altermagnetism has recently emerged as a third fundamental class of magnetism [1], with spin-spilt bands but no net magnetisation. This magnetic state is considered the “best of both worlds”, with properties of both ferromagnets and antiferromagnets which are particularly interesting for spintronic applications [2] and fundamental research. Key to altermagnetism is rotational symmetry between flipped magnetic moments, which makes understanding the precise magnetic structure of utmost importance. Muon spin spectroscopy ($\mu$SR) measurements can provide information that is complementary to, and unique from, other probes. In this talk I will present how we are using $\mu$SR to probe altermagnets. I will discuss a number of materials, including Co$_{1/4}$NbSe$_2$ [3], a $g$-wave altermagnet, and MnTe [4], which is perhaps the best studied altermagnet to date. Our measurements reveal the sometimes-unexpected magnetic structure of candidate altermagnetic materials, and test some of the key predictions of altermagnetism. Our results have important implications for technological applications of these materials.

[1] L. Šmejkal et al., Sci Adv. 6, eaaz8809 (2020)
[2] L. Bai et al., Adv. Funct. Mater. 2024, 2409327 (2024)
[3] J. N. Graham, T. J. Hicken et al., Phys. Rev. Research 8, 023361 (2026)
[4] T. J. Hicken et al., arXiv:2507.14710 (2025)

Speaker: Hicken, Thomas James (PSI - Paul Scherrer Institut)

11:00 Visualising altermagnetic domains through X-ray magnetic circular dichroism

Altermagnets exhibit compensated magnetic order with broken time-reversal symmetry, offering new opportunities for spintronics. However, the properties of bulk altermagnets remain largely unexplored at the nanoscale, highlighting the need for spatially resolved measurements.

Here, we investigate the nanoscale domain structures of two representative altermagnets, $\alpha$-MnTe and $\alpha$-Fe$_2$O$_3$ (hematite), using X-ray magnetic circular dichroism (XMCD). Combining spatially resolved spectroscopy with theoretical calculations allows
us to examine how the observed contrast reflects the underlying magnetic order.

Both materials exhibit finite XMCD, with an altermagnetic origin supported by theoretical calculations. In hematite, the Morin transition reorients the N\'eel vector---the direction of antiferromagnetic order---from the basal plane to the crystal $c$-axis. This reorientation makes XMCD symmetry-forbidden within the domains for X-rays propagating along the $c$-axis, while a finite local signal persists at domain walls with in-plane spin configuration. These observations reveal spatially distinct responses within the same material and highlight the importance of nanoscale imaging for understanding altermagnets.

Our results establish a route to visualising altermagnetic domains and motivate future studies of domain control, linking nanoscale magnetic textures to transport and optical responses.

Speaker: Yamamoto, Rikako (ETH)

11:20 → 12:20 Plenary talk: Why are there so few non-altermagnetic antiferromagnets?

Conveners: Müller, Markus (PSI - Paul Scherrer Institut), Spaldin, Nicola A. (Materials Theory, ETH Zurich)

12:20 → 13:30 Lunch @ Gartensaal

13:30 → 14:30 Contributed talks: Session 2

Convener: Sigrist, Manfred (ETH Zurich)

13:30 Simulating laser-driven material dynamics

I will present an approach for simulating the real-time dynamics of materials strongly driven by laser excitations, focusing on excited phonons. Driving phonon modes into the nonlinear regime can induce a wide range of structural and functional responses [1], but describing these dynamics at finite temperature remains challenging. While first-principles modeling has provided valuable insights, the commonly used coupled-oscillator approach requires numerous higher-order coupling coefficients, limiting its scalability to realistic materials [2], and does not explicitly account for finite-temperature effects.

Our machine-learning interatomic potential (MLIP)-based approach combines laser-driven molecular dynamics with a direct description of the anharmonic lattice, naturally capturing higher-order phonon coupling and finite-temperature dynamics without explicit parametrization of the anharmonic potential. I will demonstrate the approach for linearly and circularly driven IR- and Raman-active phonons across a range of materials, revealing their nonlinear dynamics and coupling and their potential for controlling functional properties.

[1] A. S. Disa, T. F. Nova, and A. Cavalleri, Nat. Phys. 17, 1087 (2021).
[2] A. Subedi, A. Cavalleri, and A. Georges, Phys. Rev. B 89, 220301 (2014).

Speaker: Pols, Mike (ETH Zurich)

13:50 Time-resolved circular ionic motion and its associated magnetism

Recently, phonons carrying angular momentum have presented a fascinating platform to study the coupling between lattice and spin degrees of freedom. Herein, I will present our recent work on EuTiO$_3$, an inorganic perovskite hosting localized (S = 7/2) Eu$^{2+}$ magnetic moments, where we use ultrafast X-ray experiments to directly probe the structural and magnetic response to intense circularly polarized terahertz (THz) excitation. The material has a THz-helicity-dependent optical response, similar to previous experiments on related compounds in the literature. However, our time-resolved X-ray magnetic circular dichroism (XMCD) measurements reveal no clear signatures of a transient spin-polarization, allowing us to put upper bounds on the size of a possible non-equilibrium magnetization. In parallel, with time-resolved X-ray diffraction, we directly observe the circular ionic motion of the driven phonon and quantify its associated angular momentum. The calculated magnetic moment from this classical contribution is many orders of magnitude lower than the limits provided by XMCD, revealing a discrepancy with the large magnetic response inferred from some optical experiments.

Speaker: Allington, Clifford (Paul Scherrer Institut)

14:10 Quantum geometry in 2D electron systems

The quantum geometry of electronic wavefunctions can drive unique transport phenomena. An archetypal example is the Berry curvature-induced anomalous Hall effect. Beside the Berry curvature, another geometrical structure – the quantum metric – has recently come to the fore as a core ingredient of nonlinear transport. However, experimental evidence for quantum metric-driven transport effects and, more generally, for the quantum metric remains limited to few materials. Here, we predict and demonstrate that spin-momentum-locked bands allow for an intrinsic, time-reversal odd, quantum metric magnetoresistance (QMMR) in 2D electron systems. We show that the QMMR can be probed in the Rashba 2D electron gas at the SrTiO3/LaAlO3 interface and in the Dirac surface states of the 3D topological insulators Sb2Te3. Further, we demonstrate that the quantum metric and QMMR can be controlled with gate voltages in field-effect devices. Because the QMMR originates from spin-momentum locking, it provides new means to probe angular momentum textures in momentum space. Moreover, as the quantum metric can induce nonlinear spin currents and nonlinear spin magnetization, our findings open the door to the nonlinear generation and transport of angular momentum.

[1] G. Sala, Phys. Rev. Lett. 131, 156703 (2023)
[2] G. Sala, Science 389, 6762 (2025)

Speaker: Dr Sala, Giacomo (PSI - Paul Scherrer Institut)

sala_PSIretreat_2026_red.pdf

14:30 → 15:00 Flash talks: Flash talks (even)

15:00 → 16:20 Poster session: Poster session (even/red) with coffee @ Gartensaal

15:00 Advanced Neutron Scattering Techniques to Study Nanoscale Magnetic Materials

The study of materials in reduced dimension opens a variety of opportunities to find new physics, be it by finite size effects, interfaces to other materials or the interaction between separate entities on the nanoscale. Accessing magnetic order of particles or burried films can be chellanging and there are only few methods to be used.
I will present how neutron reflectometry, diffraction and grazinig incidence scattering can be used to access magnetic depth profiles, nanoparticle magnetic structure factors and anti-ferromagnetic order hardly accessible by other techniques. Especially for the most chellanging systems the outcome crucially depends on choosing the sample structure carefully. Another important part is the modeling of the system to extract most information.
I will present examples from complex oxide heterostructures with coupled FM/AFM orders and 2D lattices of permalloy cylinders to illustrate the capability of the techniques.
With the start-up of the European Spallation Source in the near future, such capabilities will further be expanded to smaller signals and samples the PSI can exploit early on due to our contribution to the relevant instruments like the focusing reflectometer Estia.

Speaker: Glavic, Artur Gregor (PSI - Paul Scherrer Institut)

15:00 An unconventional Hall effect and devil's staircase in UAgBi2

The anomalous Hall effect (AHE) is a transport fingerprint of magnetic order, making materials with field-tunable magnetic phases a natural testing ground for it's origin. One such case arises when competing exchange interactions along a single axis generate a "devil's staircase" of distinct magnetic phases.

We investigate the microscopic origin of an unconventional AHE in the metallic actinide magnet UAgBi2, realizing such a staircase of field-and temperature dependent magnetic phases.

With neutron diffraction we mapped out the magnetic phase-diagram to compare with Hall transport measurements. We plan to refine the magnetic structures and construct an effective microscopic spin exchange Hamiltonian and validate it against the phase diagram with Monte Carlo simulations.

So far, our single-crystal diffraction has revealed competing commensurate propagation vectors $k=(0,0,1/4),(0,0,1/2)$ at zero field on cooling. Applying a field along the $c$ axis introduced magnetic Bragg peaks near $k\approx(0,0,1/3)$, sliding continuously towards $k=(0,0,1/4)$ upon warming. No in-plane magnetic component was observed, disfavoring a static topological spin structure as the source of the unconventional AHE.

Clarifying the origin will require distinguishing between dynamic real-space spin chirality and momentum-space electronic-structure effects as origins of the anomalous contribution.

Speaker: Kirchner, Kilian (PSI - Paul Scherrer Institut)

15:00 Atomic motion of an electromagnon in multiferroic TbMnO3

Multiferroics combine ferroelectricity and magnetism, enabling direct magnetoelectric coupling between lattice and spins. In TbMnO₃, a polarisation emerges from an inversion-symmetry-breaking spin cycloid, allowing electric-field control of magnetic order through coherent THz excitation. We investigate the microscopic lattice response and mode-selective coupling underlying dynamical multiferroicity in TbMnO₃.

We use femtosecond X-ray diffraction at a free-electron laser to track the time-dependent response of a comprehensive set of Bragg peaks following THz excitation. Combining these measurements with DFT calculations allows us to identify the atomic eigenvectors and quantify spin-lattice coupling.

The resonantly driven electromagnon mode, which emerges below 28 K, exhibits a pronounced structural component. The measured Bragg-peak dynamics reveal the corresponding ionic motions and provide a mode-resolved picture of the coupled spin-lattice response. From changes in magnetic exchange interactions, we determine the effective magnetic field induced by the excitation and relate it to changes in polarisation and magnetisation determined from previous time-resolved X-ray studies of the magnetic spiral. This provides direct experimental determination of the dynamical magnetoelectric coupling.

These results establish a quantitative framework for determining the time-dependent magnetic interaction Hamiltonian and advancing ultrafast control of coupled spin and lattice degrees of freedom.

Speaker: Grimes, Michael Tómas (PSI - Paul Scherrer Institut)

15:00 Collective low-energy spin excitations in antiferromagnetic spin-3/2 chains

Magnetically 1D materials are an exciting opportunity to study spin-physics at reduced dimensionality. They serve as ideal model systems and may find applications in spintronics or as quantum materials.
It is desireable to address the spin directly with atomic precision feasible by using Scanning tunneling spectroscopy.
We fabricate 1D metal organic chains consisting of Co atoms linked by a small ligand, padded by non-magnetic Ni atoms. A previous study has established that the Co atoms are S=3/2, strongly antiferromagnetically coupled and with a defined magnetic anisotropy. Scanning probe microscopy is used to address the Co atoms one-by-one and to reveal its low-energy spin excitation.
Two Co atoms embedded in a Ni chain exhibit fundamental excitation, whereas longer chains exhibit strong excitations at the beginning and end respectively. These disperse towards the center of the chains.
Our results reveal the collective excitation of spin at the atomic scale and pave the way towards engineering spin-based quantum materials by bottom-up assembly.

Speaker: Hensky, Céline (PSI - Paul Scherrer Institut)

CoQDI spin 32-chains.pdf

15:00 Comparative RIXS and Raman Study of Excitations in 5d1 Double Perovskites with Multipolar Order

Materials that show multipolar order, previously dominated by 4f and 5f elements, have attracted renewed interest with 5d1 and 5d2 electronic configurations. The breaking of local symmetry in Ba2NaOsO6 and resonant scattering of x-rays in Ba2MgReO6 strongly support the hypothesis of two order parameters. This arises from a ground-state quartet, with charge quadrupole order splitting it into two doublets while the remaining Kramers’ degeneracy is lifted through ordering of magnetic dipoles at lower temperatures. Each degeneracy lowering should carry one Rln2. One of the outstanding puzzles in these materials is related to the experimental evidence acquired on both compounds indicating that the total entropy amounts to only Rln2 across both transitions. Additionally, RIXS experiments revealed a feature around ~100meV which has been associated with the dynamic Jahn-Teller effect.
Here we present recent results where we directly compare excitations observed by RIXS and Raman spectroscopy. We find strong evidence that the RIXS feature, previously associated with the dynamic Jahn-Teller effect, is a breathing A1g Raman mode characteristic of all double perovskites. This naturally explains its invariance across both transitions but at the same time restores the entropy puzzle and calls for further spectroscopic studies of these multipolar systems.

Speaker: Dr Zivkovic, Ivica (EPFL)

15:00 Controlling magnetism with ions: New opportunities for in-memory computing

Von Neumann computing architectures form the basis of most integrated circuits used in modern computers. One of the major bottlenecks, however, is the physical separation of memory and processing units, which severely limits energy efficiency. In-memory computing has emerged as a promising alternative to overcome this challenge. In this context, magnetic materials are particularly attractive because they offer both information processing and storage within the same unit, enabling energy-efficient, non-volatile operations. A promising avenue for controlling the magnetic state in these systems is through voltage-driven ionic modulation. Here, we present solid-state magnetoionic devices combining non-volatile memory, analogue programmability and nonlinear time-dependent dynamics for unconventional computing. As a step toward practical hardware, we have scaled these devices to nanopatterned magnetic elements and established routes toward all-electrical writing, readout, tuning and interconnection, paving the way for integrated magnetoionic computing platforms.

Speaker: Ameziane, Maria (PSI & ETH Zurich)

15:00 Criticality on the Fuzzy Sphere

Continuous phase transitions exhibit universal behavior largely independent of microscopic details. A quantitative characterization of this universality requires going beyond critical exponents to the broader data defining the underlying conformal field theory.

We investigate three-dimensional quantum critical points using the fuzzy sphere, a finite-dimensional regularization of quantum systems on spherical geometry. Combining tuned microscopic Hamiltonians with exact diagonalization and density-matrix renormalization group calculations, we extract universal data from low-energy spectra and correlation functions.

We apply this framework to interacting quantum rotor models exhibiting Heisenberg, XY, and multicritical behavior, together with their gauged O(N)/Z₂ counterparts. Finite-size extrapolations yield scaling dimensions and operator-product-expansion coefficients, including quantities difficult to access with conventional numerical methods. The results agree well with complementary approaches, including Monte Carlo simulations, conformal bootstrap, and perturbative field theory.

These results establish the fuzzy sphere as a versatile numerical framework for probing strongly interacting critical and multicritical points, their gauged counterparts, and their universal properties in three dimensions.

Speaker: Dey, Arjun (PSI - Paul Scherrer Institut)

15:00 Development of Suspended Graphene Edges for Field-Emission Devices

Cold field-emission electron sources with high brightness and low energy spread are essential for atomic-resolution electron microscopy, electron holography, and coherent diffraction imaging. Two-dimensional (2D) materials offer promising emitter candidates because their atomically thin edges can provide strong field enhancement, but practical implementation has been limited by poor reproducibility, uncontrolled emission-site geometry, and fabrication complexity.
In this work, we developed a silicon-compatible microfabrication process for suspended graphene edge field emitters with lithographically defined emission sites. Chemical-vapor-deposited graphene on SiO₂/Si is patterned into suspended bridges, and the resulting structures are characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning-anode field-emission measurements.
The graphene remains intact throughout processing, while scanning-anode measurements confirm that emission is localized to the exposed edges of the suspended bridges. Using the optimized process, field emission is observed from 20 of 21 tested devices, corresponding to a functional device yield of 95%. We further demonstrate the transferability of the architecture to another 2D material by observing field emission from a proof-of-concept MoS₂ device.
These results establish suspended 2D-material edges as a high-yield platform for spatially defined field emission and a pathway toward integrated, reproducible 2D-material electron sources.

Speaker: Hajibaba, Soheil (PSI - Paul Scherrer Institut)

15:00 Dielectric spectrosocpy in Pr2Hf2O7

Rare-earth pyrochlores host a rich landscape of correlated states arising from geometric frustration and strong anisotropy. Among them, Pr₂Hf₂O₇ has emerged as a promising candidate for a quantum spin ice. While its magnetic properties have been extensively investigated, its dielectric response remains unexplored.
In this work, we probe the low-temperature dynamics of Pr₂Hf₂O₇ using broadband dielectric spectroscopy down to the sub-Kelvin regime. By measuring the complex dielectric permittivity as a function of temperature and frequency, we identify a pronounced relaxation feature evolving across the investigated temperature range. The characteristic response exhibits a clear frequency dependence and can be parameterized by a temperature-dependent relaxation time.
The observed behavior points to slow collective dynamics coupled to the electric degrees of freedom. We discuss possible microscopic origins in the context of frustrated magnetism and highlight the sensitivity of dielectric probes to low-energy excitations in these systems.
Our results demonstrate that dielectric spectroscopy provides a complementary window into the dynamical properties of frustrated rare-earth pyrochlores and opens new perspectives for investigating emergent excitations at low temperatures.

Speaker: Decrausaz, Brigitte (PSI - Paul Scherrer Institut)

15:00 Dopant-based semiconductor quantum devices

Shallow dopants in silicon and germanium weakly bind carriers in hydrogenic potentials, whose excited Rydberg states have effective Bohr radii that extend over several nanometres. These shallow dopants offer a promising platform for quantum computing, akin to neutral atom quantum computing, while also having potential for exotic devices, such as single-electron transistors. Tuning the dopant density of low-dimensionally confined dopant layers enables the creation of single-atom ordered arrays, quantum dots, 2DEGs/2DHGs, and 1D and 2D electrical gates. New fabrication techniques are enabling the creation of more advanced and scalable dopant-based devices. This work explores the potential of dopant-based semiconductor quantum devices, and the opto-electrical techniques that will be used in characterising these newly fabricated devices. Currently, photothermal ionisation spectroscopy is used to determine dopant densities and upper bounds on delta-layer thickness. Time-resolved THz spectroscopy probes the dynamics of bound carriers, such as the orbital lifetimes of the Rydberg states, and enables basic optical control, such as spin initialisation. Low-temperature magnetotransport measurements with a dilution refrigerator will be used to elucidate carrier dynamics, such as mobility, in the dopant delta layers. Characterising these devices works towards the ultimate aim of electro-optical coherent control of dopant-based semiconductor quantum devices.

Speaker: Sidhu, Adrian Parveet James (PSI - Paul Scherrer Institut)

15:00 Electronic heterogeneity in Fe5-δGeTe2 revealed by spatially resolved ARPES

Fe$_{5-\delta}$GeTe$_2$ is a near-room-temperature van der Waals ferromagnet whose electronic and magnetic properties are highly sensitive to Fe(1)-site configuration and thermal history. However, reported photoemission spectra and their structural assignments remain difficult to reconcile.
Here, we use spatially resolved angle-resolved photoemission spectroscopy (ARPES) to investigate multiple crystals prepared under different growth and thermal conditions. Spatial ARPES scans reveal three distinct spectral classes coexisting on one single cleaved surface, with individual regions extending approximately 100 μm. By mapping Fe 3p, Ge 3d and Te 4d core-level over the same surface region, we establish their spatial correlations with the low-energy band dispersions, which provide an additional fingerprint for evaluating candidate atomic configurations. Our observations show that thermal history alone does not uniquely select a single local spectrum.
While the atomic configurations corresponding to these spectral classes remain to be established, these combined measurements provide experimental constraints for ongoing structural modelling and first-principles calculations by our theory collaborators. Our results highlight the importance of spatial resolution for interpreting electronic structure in layered magnets.

Speaker: Yang, Guowei (PSI - Paul Scherrer Institut)

15:00 EUV-induced Hydrogen Desorption Lithography: A Step towards Scalable Quantum Devices in Silicon

Dopant-based qubits in silicon provide a route to compact and stable quantum devices without the need for gate-defined confinement. However, their realization requires precise control over dopant placement at the atomic scale.

Hydrogen desorption lithography (HDL) enables such control, but atomic-precision STM-based HDL suffers from low throughput. We aim to combine extreme ultraviolet (EUV)-based HDL with STM-based HDL for scalable quantum device fabrication.

To enable this research, a new end station is being developed at the SLS to allow in-situ EUV HDL, doping, incorporation, and epitaxial encapsulation within an ultra-high vacuum (UHV) environment. It will connect to the PEARL beamline, providing access to STM and XPS/ARPES for further surface analysis.

In a proof-of-concept experiment, we demonstrated large-area HDL using EUV illumination, with desorption attributed to photon-generated secondary electrons. Building on this, we now aim to establish the resolution limit of EUV-based HDL across different patterning methods such as interference lithography for periodic patterns and direct writing using Bessel beams or Fresnel zone plates for arbitrary shapes.

These developments aim to demonstrate the first EUV-based fabrication of dopant-based devices in silicon, bridging atomic precision and scalable manufacturing for Si-based quantum technologies.

Speaker: Schrago, David (PSI)

15:00 Evolving Magnetic and Electronic Phases of a High Entropy form of RMn6Sn6

The kagome $R$Mn6Sn6 material family has garnered significant interest, in part, as high-temperature magnets with a rare-earth ($R$) dependent magnetic ordering and anisotropy. This motivates synthesizing and studying high-entropy forms of $R$Mn6Sn6 to examine how the interplay of several rare-earth elements leads to different, possibly novel, magnetic states in a single crystal. Here, we present a rare-earth mix of Tb, Dy, Ho, Er, Tm, and Lu that produces phase transitions from a paramagnet to an easy-plane ferrimagnet (FiM), to a FiM easy-axis state, to a canted FiM ground state. This behavior is consistent with previously reported high-entropy $R$Mn6Sn6 compounds; however, uniquely, the rare-earth mix studied here exhibits a broad transition from easy-plane to easy-axis anisotropy from 270 K to 170 K, and reveals a nonmonotonic magnetoresistance. Using neutron scattering data, we found that both observations correlate with an incommensurate modulated contribution to the spin state due to competing rare-earth interactions. This magnetoresistive behavior and the correlated spin structures underscore the potential for rare-earth engineering of magnetism in this material family.

Speaker: Fruhling, Kyle (ETH Zurich)

Fruhling_Poster.pdf

15:00 Exploring intertwined quantum states in 132 kagome metals: LaRu3Si2 & YRu3Si2

The interplay between superconductivity and normal-state electronic response is a central question in condensed matter physics, with kagome systems offering a unique platform for exploring the relationship between intertwined electronic orders arising from their complex band structure. Recently, Ru-based 132 kagome superconductors have emerged as an intriguing alternative to the extensively studied AV3Sb5 family. Our high-pressure studies on LaRu3Si2 revealed an exceptional positive correlation between multiple quantum states (http://doi.org/10.1038/s41467-025-61383-z), motivating the exploration of alternative tuning routes.

Here, we investigate the role of "chemical pressure" via substituting La with Y, reducing the superconducting temperature by half, while shifting the charge order onset to 800 K, unprecedented in kagome systems and quantum materials more broadly. Furthermore, muon spin spectroscopy identifies time-reversal symmetry breaking and field-induced magnetism deep inside the charge-ordered state (http://doi.org/10.1038/s41467-025-67881-4).

Uniaxial compression allowing for selective lattice-symmetry breaking provides a complementary approach to hydrostatic pressure. In-kagome-plane stress in LaRu3Si2 leads to pronounced enhancement in magnetoresistance accompanied by a modest increase in superconducting temperature, further highlighting the positive correlation between superconducting and normal states (http://doi.org/10.1002/adma.74067).

Supported by DFT calculations, these findings establish a link between superconductivity, normal state, and the electronic structure, offering insights into the superconducting mechanisms in 132 kagome metals.

Speaker: Král, Petr (PSI Center for Neutron and Muon Sciences)

15:00 Finite-range polar correlation above ferroelectric transition temperature

Ferroelectricity, or ferroic polar order, emerges from a polar phonon instability below a characteristic ferroelectric transition temperature. However, dynamic and local polar order can also persist above the ferroelectric transition temperature. While its emergence is often attributed to crystal anharmonicity, the microscopic origin and temperature-dependent behavior remain unclear. We investigate how local and dynamic polar correlations emerge and evolve with temperature in quantum paraelectric materials, employing machine learned interatomic potentials to perform molecular dynamics simulations over length and time scales inaccessible to density functional theory simulations. These simulations allow us to characterize the spatial and temporal extent of polar correlations and their evolution with temperature. We further analyze the interatomic force constants required to reproduce the observed lattice dynamics, providing an interpretable connection between the microscopic interactions and the resulting behavior. Our results provide interpretable description of local polar correlation from the underlying lattice dynamics and phonon behavior, establishing a framework for connecting interatomic interactions, phonon dynamics, and dynamic polar behavior above ferroelectric transition temperatures.

Speaker: Jung, Seongjoo (ETH Zurich)

15:00 Giant Coercivity and Critical Temperature in a Compositionally Tunable 2D Ferrimagnet

Compositionally tunable ferrimagnets allow unprecedented control, making them promising for spintronics. Despite more than 100 years of research on Ising-physics, interesting fundamental realizations are still vastly underexplored: in ferrimagnetic lattices, it is predicted that in the antiferromagnetic-dominant regime the critical temperature reaches a maximum at an intermediate composition, exceeding those of its pure constituents. Despite the potential relevance of this effect toward applications, it has yet to be experimentally realized.
Here we report on a metal-organic 2D lattice where different elements (Fe and Ni) can be substituted without affecting the lattice parameters: FexNi1-xTCNE. The 2D materials class is characterized by scanning probe microscopy (SPM), x-ray magnetic circular dichroism (XMCD) and Metropolis-Monte Carlo Ising modelling.
Experimentally it is found that both Fe- and NiTCNE are 2D single-layer ferromagnets and that FexNi1-xTCNE is a 2D ferrimagnet, whose total moment can be controlled and completely compensated. As expected for such systems, the coercive field is greatly enhanced near the compensation composition, setting up a new record for such materials. The exciting observation is that also the critical temperature presents a 3.5-fold enhancement compared to the strongest constituent.
Our work demonstrates antiferromagnetic-dominant ferrimagnets, establishing an experimental realization of this theoretically proposed class of materials.

Speaker: Wäckerlin, Christian (PSI - Paul Scherrer Institut)

15:00 Is the surface of MnTe altermagnetic?

Altermagnetism is a recently discovered new form of collinear magnetic order characterized by a non-relativistic spin texture in a non-magnetic host material. There is an ongoing debate as to how much the altermagnetic electronic structure is affected by the symmetry breaking at the surface of a crystalline sample. Besides the theoretical considerations, this has implications on the interpretation of surface sensitive measurements as well as on the application of altermagnetic thin films in spintronic devices. In view of these challenges, this contribution presents a detailed STM, XPS and ARPES study of the atomic and electronic structure of exemplary $\alpha$-MnTe(0001) surfaces grown by molecular beam epitaxy on widely used substrates, SrF$_2$ and InP. Only the SrF$_2$ gives rise to a clean and highly symmetric surface, exhibiting a $2 \times 2$ reconstruction. Whereas the surface of MnTe grown on InP is actually covered by a stable InTe layer acting as a surfactant.

Speaker: Muntwiler, Matthias Kurt (PSI - Paul Scherrer Institut)

poster-cmretreat2026-muntwiler-75.pdf

15:00 Magnetic and electronic structure of strained Ba-doped ultrathin manganite films

The mixed valence manganites continue to raise much interest on account of their rich functional properties. A challenge remains the reduced electronic properties with decreasing thickness, with the notable exception of Ba-doped LaMnO3, which exhibits enhanced magnetic and electric properties at reduced film thickness, a behaviour that remains to be fully explained. Here, we study the electronic structure of 12 unit cells (u.c.) La0.9Ba0.1MnO3 (LBMO) films deposited on different substrates using XAS and soft x-ray ARPES. The XAS results show a nearly isotropic orbital occupancy for LBMO/SrTiO3, consistent with its optimal electronic properties, while SX-ARPES reveal a band structured composed of both electron and hole pockets, highlighting the complex charge distribution in the system. Estimates of the charge carrier densities give ~0.1/u.c. for the electron pockets and ~0.5/u.c. for the hole pockets, much higher than the expected 0.1 but consistent with the electronic properties. Our results show that the enhanced properties of ultrathin LBMO films arise from isotropic orbital occupancy and a charge redistribution that enhances the hole carrier density at the Fermi level to well above the nominal chemical doping. Our electronic structure characterisation provide important insights to enhancing the electronic properties of this class of complex oxide materials.

Speaker: Fernandes Vaz, Carlos Antonio (PSI - Paul Scherrer Institut)

15:00 Magnetic and Spin-orbital Excitations in Semimetallic SrIrO$_3$

The Ruddlesden-Popper iridates Sr$_{n+1}$Ir$_n$O$_{3n+1}$ evolve from the J$_{eff}$ = ½ antiferromagnetic insulators Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$ to the semimetallic perovskite SrIrO$_3$. This insulator-metal transition (IMT) is governed by the interplay between strong spin-orbit coupling, dimensionality, and electronic correlations. While the insulating members have been extensively investigated by Ir L$_3$-edge RIXS, the fate of their magnetic and spin-orbital excitations on the metallic side of the phase diagram has remained unresolved.
We address this question using RIXS on a series of [(SrIrO$_3$)$_m$ /(SrTiO$_3$)$_l$] heterostructures that span the metallic side of a confinement-driven IMT and approach the bulk SrIrO$_3$ limit. In all samples, we observe a low-lying collective magnetic mode with an antiferromagnetic dispersion resembling that of the Mott insulators, but with a large gap and larger linewidth. At higher energy, we find the spin-orbit exciton, also strongly broadened, but with an inverted dispersion and doubled periodicity reflecting the dominant role of charge fluctuations.
Our results reveal the simultaneous presence of two apparently contrasting excitations: an insulator-like antiferromagnetic pseudospin-wave and a metallic-like spin-orbit exciton. This coexistence survives deep into the metallic regime, showing that strong pseudospin and charge fluctuations are intrinsic ground state properties of perovskite SrIrO$_3$.

Speaker: Paris, Eugenio (PSI - Paul Scherrer Institut)

15:00 Magneto-transport of the kagome ice compounds HoAgGe and ErAgGe

Kagome spin ice with in-plane Ising moments have recently been reported in HoAgGe and attracted significant attraction due to field-induced magnetization-plateaus and metamagnetic-transitions involving the different spin configurations. How these discrete spin configurations are imprinted on charge transport, and whether related behavior survives in other RAgGe members, is largely unexplored. We revisited the χ(T), M(H), and magnetoresistance (MR) characteristics of HoAgGe single crystals and compared it with ErAgGe crystal. The lab-grown crystals were measured with the magnetic field along the b-axis in the kagome plane. In HoAgGe, the magnetization plateaus are observed at n/6th of the saturated magnetization, and the dM/dH shows the metamagnetic transitions coincide with the anomalies in the MR. The ErAgGe shows no magnetization plateaus at the temperature that we could reach (~2 K) but a similar sign change of MR behavior above 30K has been observed. In both compounds the largest negative MR occurs at the respective ordering temperature, indicating critical spin-fluctuation scattering. Below $T_N$, the low-field magnetoresistance of ErAgGe resolves reproducible step-like features which are not evident in magnetization. These results establish magneto-transport as a sensitive probe of field-induced spin reorganization across the RAgGe family and identifying the low-field ErAgGe anomalies remains an open question.

Speaker: BISWAL, BUBUNU (PSI, Switzerland)

15:00 Microscopic Origin of orbital Excitations in PrAlGe and CrPS$_4$ probed by Core-Level X-ray Spectroscopy

Understanding how magnetic phase transitions in correlated quantum systems respond to external perturbations requires a many-body description of localized states and ligand coordination. These macroscopic states emerge from a subtle interplay between crystal-field effects, spin-orbit coupling, and strong electronic correlations, core-level techniques like X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) take relevance. As element-specific probes, XAS and RIXS directly measure local cluster physics, core-hole multiplets, and crystal-field excitations. This provides a microscopic view of magnetism that complements macroscopic transport measurements; while transport probes the anomalous Hall effect from delocalized conduction states, XAS and RIXS target localized orbitals to extract direct information about local magnetic moments.
To capture these dynamics, we developed a theoretical framework that maps first-principles Density Functional Theory calculations to construct an Anderson Impurity Model (AIM) for localized subspaces, focusing on the 3$d$ shell for transition metals and the 4$f$ shell for rare earths. We use Dynamic Mode Decomposition to discretize the hybridization, allowing us to mimic the host density of states with a minimal number of bath sites. By solving the resulting finite-size Hamiltonian through exact diagonalization, we compute core-level XAS/XMCD and RIXS/RIXS-MCD spectra to serve as direct fingerprints of the local magnetic states.

Speaker: Pulgarin Mosquera, Juan Felipe (University of Fribourg)

15:00 NaₓV₂(PO₄)₃ Battery Cathodes: From Vacancy Orderings to Voltage Profiles with Machine Learning and DFT+U+V

Sodium-ion batteries (NIBs) are becoming an important alternative to lithium-based technologies because of the abundance of Na. For NIBs, polyanionic compounds such as NaₓV₂(PO₄)₃ (NVP) are promising cathode candidates due to their excellent cycling stability and potential for high operating voltage.
The complex crystal structure of NVP allows for a variety of Na-ion and vacancy orderings, giving rise to multiple phase transitions during battery cycling.
To gain a better mechanistic understanding of the relationship between these orderings and the resulting battery properties, such as the voltage profile, we explore the material using machine-learned interatomic potentials (MLIPs) and density functional theory, augmented with self-consistent Hubbard corrections (DFT+U+V).
With these methods, we accurately reproduce the experimental voltage plateaus of 3.4 V and 1.6 V and are able to attribute them to the underlying Na-ion orderings and redox mechanisms. Furthermore, we find two metastable phases, one at x=2 and one between x=3.5 and x=3.75. Finally, we demonstrate the relation between local structure, oxidation states, and Hubbard parameters.
These mechanistic insights help to understand the complex energy landscape of NVP and provide a foundation for future strategies to optimize its electrochemical properties.

Speaker: Schären, Stefan (PSI (Paul Scherrer Institut))

15:00 Next-generation solid-state thin film batteries for integrated electronic systems

The continued miniaturization of electronic systems demands energy storage technologies that can be integrated with semiconductor manufacturing. Emerging applications, including the Internet of Things, wearable electronics, implantable medical devices, distributed sensors and edge artificial intelligence, require compact, safe and reliable power sources that combine high power with a minimal footprint.

At PSI, we are developing a next-generation solid-state thin film battery platform for monolithic integration with semiconductor and MEMS technologies. The platform employs an all-inorganic architecture fabricated using thin film deposition and advanced microfabrication processes. By combining high power capability, rapid charging, long cycle life and an ultra-compact form factor, it aims to bridge the growing gap between increasingly advanced low-power electronics and existing microscale energy storage solutions.

Manufacturability and system-level integration are central to the design, enabling future incorporation into highly integrated electronic platforms without compromising miniaturization. The technology could therefore support autonomous microsystems for which conventional batteries are limited by size, integration complexity or long-term reliability.

This presentation will introduce the technology, discuss the challenges of powering next-generation microsystems and highlight the opportunities offered by semiconductor-compatible solid-state thin film batteries.

Speaker: Montazerian, Mohammadhossein (PSI - Paul Scherrer Institut)

15:00 Novel “Mott metal” correlated phase in BaPbO3

Common intuition about the role of electron correlations in condensed matter is mainly shaped by the Mott-Hubbard model in the context of half-filled $d$-electron systems. There, the Coulomb interaction between two electrons occupying the same site impedes conductivity, eventually opening an insulating gap when the interaction strength, $U$, is sufficiently strong. The success of this model in capturing the essential physics of several classes of strongly correlated materials – particularly some prominent transition metal oxides, such as cuprates – lures many of us into assuming that the Hubbard $U$ interaction should universally drive systems toward insulating behavior. I will argue that this common intuition is spectacularly upended in barium plumbate. In the non-interacting picture, BaPbO₃ should be a small-gap semiconductor, but it is nevertheless experimentally well-established as a good metal. Based on ARPES experiments, DFT+U calculations, and spectral simulations, we conclude that a metallic state is intrinsic to BaPbO$_3$, where it forms due to a $U$-driven reconstruction of the O $2p$ orbitals, which partially hybridize with Pb $6s$ states. This transformation of a band insulator to a metal due to on-site Coulomb interactions represents the inverse of the Mott insulator paradigm and constitutes a new regime of correlated electron behavior.

Speaker: Plumb, Nicholas Clark (PSI - Paul Scherrer Institut)

15:00 Optimal Local Orbitals: On the Way to Accurate Wave Function Represenation

Many calculations, such as transport or optical properties, require accurate wave-functions on a dense
grid of points in reciprocal space. It is desirable not to run an electronic structure calculation for each
k-point, but to rather interpolate them from a coarse grid. Electronic structure calculations are com-
monly run using a large plane wave bases, which are inconvenient for interpolation, and current post-
processing schemes mainly focus on interpolating the band structure rather than the wave-functions.
We introduce multiple alternative basis sets that are significantly smaller and localised in real space.
We project our plane wave basis onto Atomic Orbitals(AOs), which are then further compressed. The
first method we propose are Optimal Local Orbitals, which are obtained by mixing orbitals on the
same atom so the projectability in the remaining set is maximised. The second method we showcase
are Intrinsic Atomic Orbitals, where a smaller subset of our AO basis is selected and projected into
the wave-function space of the electronic structure calculation.
We present the results of a high throughput calculation on three dimensional Elemental Structures
and Binary Oxides, calculating the projectability and interpolation quality. We further showcase the
performance of these basis sets for velocity operator calculations.

Speaker: Goutier, Ann Chantal (PSI - Paul Scherrer Institut)

15:00 PESKIT: Exploring PhotoEmission Spectroscopy from first principles

Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool to investigate the electronic structure of condensed matter in the laboratory. When irradiated by polarized light, the probed material emits electrons, whose momentum, energy, and spin can be measured in order to gain information about the material.
The connection between the measured spectrum and the underlying electronic structure is far from trivial. Bridging this gap is the aim of our first-principles based numerical approach implemented in the PESKIT code. The latter establishes this connection by computing spin-resolved ARPES spectra within the one-step model based on density functional theory calculations. A wide range of materials, from semi-infinite bulk crystals to two-dimensional materials, can be investigated using PESKIT. Among the highlights of the code are the use of first-principles scattering states instead of the widely used plane-wave approximation, and a fully relativistic treatment.
On this poster, I would like to give an introduction to the code which is soon to be publicly available, and to convince you of its capabilities by guiding you through a collection of results from systems such as two-dimensional transition metal dichalcogenides and bulk materials hosting topological surface states.

Speaker: Eilmsteiner, David (PSI Center for Scientific Computing, Theory and Data, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland)

15:00 Polarons and charge-transfer excitations from grand-canonical neural networks

Magnetite Fe$_3$O$_4$ is the oldest known magnetic material, yet the physics of its Verwey transition is still not fully solved due to its coupled structural, charge, and orbital interactions. The difficulty hinges on the multivalent nature of iron (Fe2+/Fe3+), which is a central motif in redox chemistry and functional oxides.

Machine learning interatomic potentials (MLIP) trained on DFT+U+V data have recently proven to efficiently tackle the oxidation state of multivalent metallic ions with near ab initio accuracy, adding to their intrinsic efficiency enabling the simulations of large and/or complex systems.

This is especially relevant for magnetite where the low-temperature monoclinic phase requires a large (224 atom) supercell with a combinatorial number of 64 choose 32 ~ 1018 possible charge orderings, making ab initio calculations expensive.

In this work, we train an oxidation-aware MLIP for magnetite and demonstrate its capabilities side-by-side with a conventional (unaware) fine-tuned foundational model. While the oxidation-aware potential provides the oxidation state directly as a control variable, the conventional potential can capture it intrinsically through the distinct volumes of the octahedral oxygen cages.

Speaker: Dr Vojacek, Libor (Paul Scherrer Institute PSI)

15:00 Room-temperature electrical control and structure of competing charge density wave states

Interest in metastable charge density wave (CDW) states goes beyond fundamental physics, as their electrical manipulation could enable ultra-efficient memory devices. However, non-volatile switching between CDW states using electrical pulses has been limited to cryogenic temperatures. We investigate the layered semiconductor EuTe$_4$, which exhibits coexisting stripe CDW orders. We observe that electrical pulses can excite non-equilibrium, yet stable electronic states across a broad temperature range, from 6 K to 400 K. Switching occurs through a non-thermal pathway and is reversible via thermal erasure. The resistance of the new electronic state is tunable by the pulse voltage, so the device acts as an ultraefficient memristor.
EuTe$_4$ exhibits rich physics of competing CDW states, which give rise to a broad thermal hysteresis already in the absence of electrical excitation. We are currently exploring this unconventional behaviour using single-crystal diffraction and nanodiffraction. Our preliminary experiments indicate that distinct CDW orders coexist in separate mesoscopic domains, each with well-defined internal CDW order. Resolving the domain structure provides new insight into coexisting CDW orders in EuTe$_4$ and directs us towards understanding the response to electrical excitation.

Speaker: Venturini, Rok (PSI - Paul Scherrer Institut)

15:00 Scanning Transmission Soft X-ray Spectro-Microcroscopy

Nanoscale mapping of materials properties is an important part of condensed matter research. Scanning transmission soft X-ray spectro-microscopy (STXM) can provide nanoscale imaging with contrast based on a variety of soft X-ray spectroscopic effects to reveal material details for magnetism, oxidation states, molecular structure and orientation. The PolLux STXM at the Swiss Light Source has a record resolution of 7 nm and 20 years of experience investigating a broad variety of materials. In-situ, in-operando, stroboscopic dynamics and 3D measurements have each been implemented. We recently demonstrated super-sampling imaging for faster, higher resolution measurements. Further, the new SOPHIE endstation at the SIM beamline can perform STXM and ptychography with even higher performance. As "user instruments", the PolLux and SOPHIE STXMs are easily accessible.

Speaker: Watts, Benjamin (PSI - Paul Scherrer Institut)

15:00 Scientific writing, publishing and AI – What the library can offer

Lib4RI is the shared library for PSI, Eawag, Empa and WSL. We offer typical library services but also help researchers with scientific publishing in several ways.

1. Scientific writing and publishing: We offer training courses about scientific writing and publishing. During the last years, we increasingly offer consultation on the use of AI during the writing and publishing process and the regulations that need to be considered.
2. Open Access: You and your publications benefit in many ways when they are published Open Access (OA). The OA landscape can be complicated, but we can help and support in several ways.
3. Visibility for your publications: Open Access, open licences, indexation, preprints, … There are many aspects that can improve the visibility of your publications. We can ensure some of them and consult on others.
4. Indexation of your publications: DORA PSI is not just a repository to archive your publications. Having your publications listed in DORA ensures indexation in important databases, improves their visibility and completes your institutional publication list.
   Come to our poster to learn more about these aspects and why you should consider OA and AI policies already when you start writing your manuscript.

Speaker: Bachmann, Michael (Eawag)

15:00 Spectral signature of non-equilibrium, high-density incoherent excitons

The coherence of excitons, bound particle-hole pairs, is key for a number of non-equilibrium phenomena,including the amplification of ultrafast shift currents or “self-driven”exciton-Floquet effects. However, coherence is often suppressed by scattering processes on an ultrafast time scale. Still, such incoherent nonequilibrium states of excitons can have a profound impact on dynamical material properties. In this work, we investigate the effects of such long-lived non-equilibrium states for the single-particle spectral function and the signature in angle-resolved photoemission spectroscopy (ARPES). To this end, we employ the nonequilibrium Green’s function (NEGF) approach. To treat the excitons non-perturbatively, we use the particlehole T-matrix. These calculations become tractable by using an efficient compressed representation in the exciton basis.

Speaker: Moos, Katja Sophia

15:00 Spin and lattice dynamics in the two-ladder quantum magnet Cu-CPA

Quantum spin ladders are materials that bridge the gap between spin dimer and spin chain systems and can often be realized in metal-organic quantum magnets. In such compounds, presence of large organic groups allows for tunable, laboratory-accessible energy scales but also brings about low-energy phonons whose coupling to spin degrees of freedom remains poorly explored. We investigate the metal-organic compound (C$_5$H$_9$NH$_3$)$_2$CuBr$_4$ (Cu-CPA) that was recently found to contain two inequivalent spin ladders at temperatures below a structural phase transition. High-resolution inelastic neutron scattering on large deuterated single crystals enables the disentangling of the triplon spectra of the two inequivalent ladders and help us to estimate the relative strengths of their leg and rung exchange interactions. Additionally, we show that the low-energy local phonons are sensitive to the spin correlations. Finally, we test the predictions of the model Hamiltonian against the high-field magnetization and torque measurements and reveal open puzzles that might contain insights about the elastomagnetic coupling in the material.

Speaker: Arh, Tina (PSI - Paul Scherrer Institut)

15:00 Strain-tunable charge localization coupled to complex magnetic orders in EuAl4

Understanding and optimizing the coupling between localized charge modulations and magnetic degrees of freedom in strongly correlated electronic systems is of eminent interest. For this purpose, we investigate the interplay between spin and charge degrees of freedom in EuAl$_4$, a rare-earth intermetallic exhibiting a charge density wave (CDW $\approx$134 K) and a cascade of magnetic phase transitions [1]. Using Synchrotron High-Energy X-ray Diffraction, we mapped the material's structural response by tracking Bragg reflections and CDW satellites across a broad parameter space including temperature, high magnetic fields and uniaxial strain along the principal crystallographic axes. We observed a large and anisotropic coupling between the magnetic ordering vector of Eu$^{2+}$ and the charge order throughout the phase cascade. While $c$-axis strain suppresses the CDW transition temperature by approximately 10 K and increases incommensurability significantly, $b$-axis strain yields a weaker, competing response that slightly decreases both parameters. Furthermore, these findings demonstrate that mechanical strain actively controls charge order, establishing EuAl$_4$ as a model system for designing optimally coupled spin-charge phases.
[1] M. Baumgartner et. al., arXiv:2607.07544 (2026).

Speaker: Baumgartner, Mario

15:00 Superconductivity in FeSe thin films

Understanding how superconductivity changes when a material is made very thin requires separating intrinsic properties from effects caused by the interface and the surrounding environment. FeSe is a particularly interesting system in this context, as its superconducting properties are strongly affected by film thickness, the substrate, and the surface. The discovery of enhanced superconductivity in monolayer FeSe on SrTiO₃ demonstrated how powerfully an interface can influence the superconducting state. Importantly, this enhancement is not limited to the monolayer, which makes FeSe thin films a versatile platform for studying how superconductivity evolves with thickness. Their strong sensitivity to the surface environment, however, makes thin films challenging to prepare and handle, and the contributions of substrate, strain, and surface are difficult to separate. To disentangle these contributions, FeSe films are investigated systematically as a function of thickness, substrate, and growth conditions, with the aim of establishing which parameters govern the onset and stability of superconductivity. In the longer term, this understanding could open the way to alternative geometries that modify the mechanical boundary conditions and provide a clearer picture of what determines the superconducting properties of FeSe.

Speaker: Petrović, Jelena (PSI - Paul Scherrer Institut)

15:00 Synthesis and characterization of rare-earth halides

Binary rare-earth halides MX3, with X=Cl-I, are a rich family of compounds that crystallize in the UCl3, PuBr3, and BiI3 structures with space groups P63/m, Ccmm, and R-3, respectively. Their structures vary from 2D with honeycomb or distorted triangular layers to 3D with edge and face sharing polyhedra. These compounds are of interest as candidate quantum frustrated magnets and were studied by neutron experiments at low temperatures. For instance, single crystal neutron scattering data on ErBr3 have shown a magnetic phase transition to a continuously degenerate non-collinear 2D state at T = 280 mK [1], while YbBr3 does not show ordering down to 100 mK [2]. Here, we present an overview of the rich family of binary rare-earth halides, synthesis method and the Bridgeman technique as a suitable method for the growth of high-quality single crystals that are required for neutron scattering studies, as well as results of some magnetic studies.

References:
[1] Wessler, C., et al. Commun. Phys. 5 (2022) 185.
[2] Wessler, C., et al. npj Quantum Mater. 5 (2020) 85.

Speaker: Walicka, Dorota (PSI)

15:00 Ultralow-temperature rare-earth magnetism measured at the SwissFEL Cristallina experimental station

Traditionally, neutron scattering has been the main technique to study spin order and excitations, such antiferromagnetism of LiErF$_4$. However, exceptional improvements in brilliance of accelerator-based X-ray sources have elevated X-ray scattering as an effective complementary technique that enables elemental sensitivity via electronic resonance effects, as well as the ability to probe small samples.

Reaching sub-Kelvin temperatures at synchrotrons is prohibitively difficult due the heat load from the incident continuous photon beam. This effectively precludes measurements at milli-Kelvin temperatures – hence we turned to pulsed X-ray FELs.

Here we report on the recently commissioned ultralow-temperature vector magnet setup that has become available to userd at the SwissFEL Cristallina-Quantum endstation. We have used single X-ray FEL pulses for resonant magnetic X-ray scattering at the Er L$_3$-edge, showing that antiferromagnetic order of LiErF$_4$ can be detected at sample temperatures as low as $T = 35$ mK before the onset of heating. Magnetism can also be tuned via vector magnetic fields, e.g., to lift the degeneracy of magnetic domains, and the effect on the magnetic order parameter directly monitored via the X-ray signal.

This proof-of-principle demonstration of electronic diffraction-before-destruction highlights the advantage of a brilliant, ultrafast X-ray source to measure fragile quantum many-body states.

Speaker: Pedrini, Bill Francesco (PSI - Paul Scherrer Institut)

15:00 Van der Waals devices for surface-sensitive experiments

ln-operando characterization of van der Waals (vdW) devices using surface-sensitive probes provides critical insight into phase transitions and correlated electronic states. However, integrating vdW materials into functional device geometries while preserving pristine surfaces remains a central challenge, as conventional lithographic steps typically introduce contamination that limits advanced spectroscopies. We present a stencil-lithography-based fabrication scheme enabling resist-free patterning of micron-scale electrical contacts and ultra-high-vacuum exfoliation of thin flakes down to the monolayer limit. Using 1T-TaS₂ as a model system, we demonstrate devices that combine reliable electrical pulsing and transport measurements with clean surfaces suitable for angle-resolved photoemission spectroscopy and X-ray photoelectron spectroscopy (XPS).
In particular, spatially resolved microbeam XPS of the Ta 4f core level reveals pronounced differences between bulk-like and monolayer flakes. Bulk-like samples show the expected multi-component CDW lineshape, whereas monolayers exhibit a reduced overall splitting and shifted relative intensities, consistent with the absence of out-of-plane stacking in a single 1T-TaS₂ layer.

Speaker: Taufertshöfer, Nicolai (PSI - Paul Scherrer Institut)

15:00 Vertex Reconstructed muSR - High Rates and Unprecedented Lateral Resolution

Silicon pixel detectors are emerging as powerful tools for enhancing measurements in muon spin rotation/relaxation/resonance (muSR) experiments. These detectors enable tracking of muons and decay positrons providing, for the first time, vertex-reconstructed muSR (vx-muSR) with high lateral resolution. This, in turn, allows for measurements in multiple samples simultaneously, laterally resolved magnetic characterization and operation at more than tenfold the currently used rates. This addresses longstanding limitations of muSR using conventional scintillator-based systems. Recent developments demonstrate the capabilities of Silicon pixel based muSR spectrometers, opening new possibilities for studying magnetic and superconducting materials. This contribution highlights the impact of vertex reconstructed muSR (vx-muSR) on the future of the muSR technique.

Speaker: Isenring, Pascal (PSI - Paul Scherrer Institut)

15:00 √3×√3 order of ferromagnetic triangles in a short-interlayer kagome metal

We identify an unconventional mechanism for stabilizing non-collinear magnetic order in kagome-lattice materials. In a new Mn-based intermetallic compound, single-crystal neutron diffraction reveals a √3 × √3 magnetic superlattice characterized by ferromagnetic Mn triangles whose magnetic moments are oriented 120° relative to one another. These ferromagnetic units are interconnected by frustrated triangular motifs that further enhance the complexity of the magnetic structure. Although the Mn atoms form a geometrically perfect kagome lattice, the shortest Mn–Mn separation occurs between adjacent layers rather than within the kagome plane. This three-dimensional connectivity produces a distinctive hierarchy of magnetic exchange interactions. In particular, competing second- and third-nearest-neighbor couplings, strongly influenced by the short interlayer Mn–Mn distance, can stabilize the experimentally observed magnetic configuration. A minimal theoretical model incorporating these competing interactions successfully reproduces the unconventional √3 × √3 magnetic order. Our results demonstrate that frustrated in-plane and out-of-plane interactions can cooperate to stabilize non-collinear magnetism, suggesting a general strategy for discovering and designing unusual magnetic states in kagome metals.

Speaker: Pakalniškis, Andrius (PSI - Paul Scherrer Institut)

16:20 → 18:00 Contributed talks: Session 3

Convener: Zaharko, Oksana (PSI - Paul Scherrer Institut)

16:20 Nanoscale Mapping of Magnetic Orientations with Complex X-ray Magnetic Linear Dichroism

Compensated magnets are of increasing interest for fundamental research and applications because their net-zero magnetization enables ultrafast dynamics and robust magnetic order. Nanoscale mapping of local domain structures is essential for understanding and controlling this order. Here, we combine X-ray magnetic linear dichroism (XMLD), a spectroscopic technique sensitive to the local Néel-vector orientation, with ptychography, a coherent X-ray imaging technique, to obtain high-resolution images of in-plane magnetic orientations in a model sample exhibiting a Landau pattern. Combined with hierarchical clustering, an unsupervised machine learning approach, these techniques enable retrieval of the full complex XMLD spectrum and mapping of magnetic domains with sub-100-nm resolution. We show that phase contrast is significantly stronger than the corresponding absorption contrast, enabling higher-resolution imaging. This establishes phase contrast as a high-resolution mechanism for mapping magnetic orientations and paves the way toward higher-dimensional X-ray imaging, including Néel-vector orientation tomography of antiferromagnets. Hierarchical clustering further enables detailed analysis of nanoscale spectral features, with potential applications to spectroscopic analysis of intricate magnetic textures and domain selection based on time- or polarization-dependent contrast changes.

Speaker: Raboni Ferreira, Marina (ETH Zurich and Max Planck Institute for Chemical Physics of Solids)

16:40 Patterning two-dimensional gradients in structural and magnetic properties for spintronics and magnonics applications

Novel spin-based logic architectures are being developed for efficient data storage and processing. Two prominent directions include the development of in-memory computing and all-electric control of magnetic order. We have previously showed that spatial patterning of uniaxial anisotropy via selective oxidation can result in lateral coupling [1], which can be incorporated into electrically-controlled logic gates [2].

To enhance the pool of structural and magnetic properties that can be patterned, we have developed direct-write laser annealing [3]. Here, the underlying magnetic properties are linked to heat-activated processes such as crystallization, interdiffusion or oxidation. We demonstrate the capability of this technique by realization of a spin wave filter [3], domain wall auto motion for neuro-inspired computing [3,4], generation of unconventional spin-orbit torques in tungsten films [5] and patterning of TmIG films [6].

The laser annealing method opens new opportunities to pattern complex material and magnetic landscapes with high-precision, leading to further disruptive technologies in magnetism and beyond.

1. Z. Luo et al. Science (2019)
2. Z. Luo et al. Nature (2020)
3. L.J. Riddiford, J. Brock et al. Nat. Commun. (2025)
4. J. Brock et al. Nano Lett.(2026)
5. L.J. Riddiford et al. Adv. Mat. (2026)
6. L.J. Riddiford et al. Submitted(2026)

Speaker: Hrabec, Ales (1 Laboratory for Mesoscopic Systems, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland 2 PSI Center for Neutron and Muon Sciences, 5232 Villigen PSI, Switzerland)

Hrabec_CM_retreat.pptx

17:00 Artificial spin ice on the CaVO lattice: a bridge from square to kagome

Artificial spin ices are arrays of dipolar-coupled nanomagnets behaving as Ising spins. They have been powerful platforms to directly image phase transitions and complex correlations. Studies have so far concentrated on the square and kagome lattices, whose ground states (simple antiferromagnetic order and a fragmented Coulomb phase, respectively) sit at opposite ends of the frustration spectrum.

Here we characterize the thermodynamics of an artificial spin ice on the CaVO (square-octagon) lattice, an Archimedean geometry that lets us continuously interpolate between these two regimes within a single system.

By varying the relative size of the square and octagonal plaquettes, we continuously tune the vertex-level interactions. We map the resulting phase diagram numerically using Monte Carlo simulations, and experimentally with magnetic force microscopy and temperature-dependent magnetometry.

We find two distinct ground states, each resembling either the square or kagome phenomenology, separated by a multicritical region hosting several spin liquid states and, in some geometries, moment fragmentation. Magnetometry alone can detect these correlated phases without large-scale instrumentation.

This work shows that frustration can be engineered within a single lattice, offering a route to exotic magnetic phases (like spin liquids or multicriticality) at the mesoscale, without extreme pressure, field, or temperature.

Speaker: Museur, Flavien Guillaume (Laboratory for Mesoscopic Systems, ETH - Center for Neutron and Muon Sciences, PSI)

17:20 The effect of frustration in metallic HoInCu4 and ErInCu4

Magnetic frustration in materials arises from magnetic interactions that cannot be satisfied simultaneously, originating from constraints of the lattice geometry or conflicting interactions. The resulting degeneracy between frustrated ground-state configurations can lead to strong fluctuations, triggering unconventional (quantum) phases of matter. In insulators these phases are described often by Heisenberg or Ising Hamiltonians, but these approaches are less effective for frustrated metals, because the charge degrees of freedom can no longer be ignored. Here, we test whether we can leverage spin-only Hamiltonians to describe the microscopic behavior of metals possessing a low charge density at the Fermi-surface and use HoInCu4 and ErInCu4 as a baseline. Our neutron scattering results show that the two materials exhibit unconventional quantum behavior, arising from nearest-neighbor interactions. However, the two materials feature distinct ground state properties, which stem from small differences in their itineracy.

Speaker: Krighaar, Kristine M. L. (PSI Center for Neutron and Muon Sciences, 5232 Villigen PSI, Switzerland)

17:40 Coherent spin waves in a maximal entropy phase

In solids, disorder is conventionally regarded as detrimental to coherence. It typically localizes and dampens collective excitations, as exemplified by Anderson localization or the broadening of magnetic modes in systems lacking long-range order. While high-entropy materials are specifically designed to harness disorder and stabilize homogeneous mixed-phase structures that can display unique properties, this same disorder is nonetheless expected to preclude the formation of coherent magnetic excitations.
To test the limits of this picture, we selected the antiferromagnetic system YBaCuFeO$_5$, as it features two distinct transition metal atoms with significantly different magnetic moments, rendering its spin dynamics exceptionally sensitive to local atomic ordering.
Combining resonant inelastic x-ray scattering and linear spin wave theory, we reveal a surprising paradox: YBaCuFeO$_5$ exhibits an unexpected, entropy-driven mixed phase, in which disorder, rather than reducing the lifetime of the collective excitations, favors coherence [1]. In this mixed phase, the spin waves remain dispersive, markedly distinct from those expected for an ordered ground state, and exhibit well-defined acoustic and optical branches separated by a large optical gap. These results demonstrate that in entropy-stabilized magnets, disorder can favor coherent collective modes previously thought to be exclusive to low-entropy systems.
[1] A. Romaguera et al., arXiv:2604.23597 (2026).

Speaker: Razzoli, Elia (PSI - Paul Scherrer Institut)

18:00 → 20:30 Apéro @ Gartensaal

18:00 → 20:30 Poster session: Open poster session @ Gartensaal

Thursday 12 November

08:15 → 08:45 Welcome & Registration @ Aula Foyer

08:45 → 09:30 Facility/infrastructure talks: Session 2

Convener: Bartkowiak, Marek (PSI - Paul Scherrer Institut)

08:45 SwissFEL

Speaker: Patthey, Luc (PSI - Paul Scherrer Institut)

09:00 QMMC

Speaker: Janoschek, Marc (PSI - Paul Scherrer Institut)

09:15 AiiDAlab - a computational facility for materials simulations and data analysis

AiiDAlab is a web platform for running materials simulations and data analysis directly from the browser. Under the hood, it is powered by AiiDA, a workflow engine whose development is coordinated in CSD and that provides robust automated workflows, full data provenance and easy access to HPC resources. In this talk, I will present the AiiDAlab platform and its deployments, including the public demo server (demo.aiidalab.io) and the instance available to all PSI staff (aiidalab.psi.ch). I will then focus on the AiiDAlab Quantum ESPRESSO app, whose plugins enable users to compute, using DFT (and soon also ML-accelerated methods), properties directly relevant to PSI experiments: phonons and inelastic neutron scattering spectra, muon stopping sites and local fields, XAS and XPS spectra, and more. I will also mention how the platform and its workflows are starting to be adopted at other facilities beyond PSI, such as STFC (UK) and TRIUMF (Canada). Next, I will discuss how AiiDAlab is now being applied, beyond atomistic simulations, to enable secure access to experimental data and their analysis. As part of an ongoing CNM–CSD collaboration, we aim to offer SINQ users a browser-based platform with all relevant software preinstalled and with access restricted to the data of their own proposals, giving them a protected environment for analysing their experiments. Initially demonstrated on the CAMEA spectrometer, the platform is now being extended to all SINQ instruments. Finally, I will outline our vision of offering routine simulations to PSI users together with their beamtime proposals.

Speaker: Pizzi, Giovanni (PSI - Paul Scherrer Institut)

09:30 → 10:30 Contributed talks: Session 4

Convener: Donnelly, Claire (ETH/PSI)

09:30 Strain-tunable charge localization coupled to complex magnetic orders in EuAl4

Charge localization is particularly interesting when coupled to antiferromagnetic spin structures. Coupled spin-charge orders are well established in elemental chromium and correlated oxide superconductors, yet the interplay between charge order and more complex magnetic textures -- such as skyrmion lattices and chiral spin structures -- remains largely unexplored. In this talk, we report a comprehensive study of how charge localization couples to the unusually rich sequence of magnetic phases in EuAl4. Using x-ray diffraction under applied magnetic field and uniaxial pressure, we demonstrate a direct coupling between the charge and spin order parameters. In the absence of external stimuli, charge localization is markedly enhanced upon entering the magnetically ordered phases. Strikingly, this effect is highly susceptible to strain: uniaxial pressure applied along the charge-order propagation direction further enhances localization, whereas pressure applied perpendicular to it weakens it. Application of magnetic field reveals both competitive and possible collaborative interactions between spin and charge order. This flexible coupling between spin and charge ordering opens a new route to designing symmetry-breaking states, including the possibility of imprinting topological charge order from chiral spin textures.

Speaker: Chang, Johan

09:50 Probing the magneto-dynamics of coherently driven spins and superconductors

Using the periodic electromagnetic field of light to coherently control materials enables the creation and control of new states of matter and interesting quantum many-body states.
Controlling solid-state spins through lightpulses is possible through a number of indirect mechanisms, like spin-orbit or spin-lattice coupling, but also directly and universally via the Zeeman interaction. A high-frequency expansion of the Floquet-Hamiltonian shows how a time-reversal symmetry breaking oscillating field gives rise to an effective static field that scales as $B^2/\omega$.
To study this, NV$^-$ centers in diamond are an excellent platform: Their very long coherence time, and the possibility of optically initializing them in a single eigenstate has been used for quantum information processing and sensing. Microwave control using 2.87GHz resonance is limited to spin rotations on the nanosecond timescale, we show that far off-resonant mid-infrared pulses can act in picoseconds. Performing state tomography to reconstruct the quantum state after interaction, opens a new range of possibilities both for exploring fundamental phenomena in light-matter coupling and ultrafast quantum sensing.
A very different system in which a magnetic degree of freedom is quantized are superconductors in multiply connected geometries. Ultrafast proximate optical magnetometry (UPOM), now gives access to the dynamics of this phenomenon.

Speaker: Jotzu, Gregor (EPFL)

10:10 Quantum optimization for materials exploration

Finding stable atomic structures is a central challenge in computational materials science, especially when rugged landscapes contain minima separated by large barriers. Quantum annealing offers an alternative to thermal exploration by exploiting quantum fluctuations to access hard-to-reach configurations.

Here, we introduce a quantum-optimization framework based on path-integral molecular dynamics (PIMD). The method is compatible with molecular-dynamics workflows and machine-learning interatomic potentials. Annealing to the classical limit provides a global optimizer, further enhanced by a replica-pinned strategy [1]; stopping instead at the physical nuclear quantumness enables quantum-informed structure search for systems with strong nuclear quantum effects, such as high-pressure hydrides [2].

We obtain remarkable results on optimization benchmarks and bulk reconstruction problems [3]. For the high-pressure superconductor LaH₁₀, the quantum-informed protocol recovers the high-symmetry structure stabilized by nuclear quantum fluctuations.

The framework therefore serves both as a tool for materials discovery and as a method to study systems where nuclear quantum effects are essential, with potential applications to other light-particle problems such as muon stopping-site determination.

References
[1] T. Gregor and R. Car, Chemical Physics Letters 412, 125–130 (2005).
[2] I. Errea et al., Nature 578, 66–69 (2020).
[3] A. Fiorentino and N. Marzari, arXiv:2606.03405 (2026).

Speaker: Fiorentino, Alfredo (PSI - Paul Scherrer Institut)

CM_retreat_12_11_2026.pdf

10:30 → 11:10 Coffee Break @ Aula Foyer

11:10 → 12:30 Contributed talks: Session 5

Convener: Gawryluk, Dariusz Jakub (PSI - Paul Scherrer Institut)

11:10 Spectroscopic Signatures in NaxMnO2 Cathodes for Na-ion batteries: A Computational Study Based on Density-Functional Theory

Layered sodium manganese oxides (Na$_x$MnO$_2$) are key cathode candidates for Na-ion batteries, yet their performance is governed by complex phase transitions, Jahn-Teller distortions, and competing cationic versus anionic redox mechanisms.
Here, we establish microscopic spectroscopic signatures capable of distinguishing local Na/vacancy ordering, Mn charge states, and oxygen redox activity in P2-Na$_x$MnO$_2$. Using density functional theory with self-consistent Hubbard U and V parameters computed with density-functional perturbation theory[1-2], we determine ground-state geometries and voltage profiles, paired with Bethe-Salpeter equation calculations of Mn and O K-edge X-ray absorption spectra (OCEAN code[3]). Hubbard paramters correctly capture Mn$^{3+}$/Mn$^{4+}$ charge ordering and Jahn-Teller distortions without empirical fitting. Stoichiometric phases display classic Mn redox with systematically shifting Mn K-edges. In contrast, cation-deficient, oxygen-rich phases exhibit high-voltage oxygen redox, characterized by a static Mn edge and emerging O pre-edge features.
This work highlights first-principles XAS simulations as a powerful diagnostic tool to decode local structural distortions and energy-storage mechanisms in functional battery materials.

Speaker: Sanella, Valentina (PSI - Paul Scherrer Institut)

SANELLA_Condensed-Matter-Retreat_Nov_2026.pdf

11:30 A physical model enables chemical control of correlated disorder in hybrid perovskite energy materials

Solution-processable hybrid organic–inorganic metal halides which adopt the perovskite crystal structure have demonstrated unexpected performance in electronics, solar cells, radiation detectors, and light emitters. However, instability and disorder pose ongoing performance and reliability challenges, hindering the application of these materials.

Additionally, fundamental questions remain about how structure determines function in this class of materials. Compared to the long-studied and diverse family of perovskite oxides, these heavy halides accommodate a different and narrower set of ions by virtue of the large size and monovalent charge of the halides, even incorporating small organic molecular cations on the larger cation site. Such molecular cations exhibit lower symmetry than the usual monatomic ones, introducing orientational degrees of freedom and anisotropic steric and hydrogen-bonding interactions that are not present in oxide analogs.

Inspired by the successes of statistical physics models for oxide ferroelectrics and dielectrics and elastic multipole expansions for describing anisotropic point defects, we developed a microscopic effective Hamiltonian designed to capture the essential interactions in many hybrid perovskites. This model reproduces key experimental observations, exhibits intriguing properties related to geometric frustration, and allows us to predict new superlattice alloy compositions which may exhibit enhanced thermodynamic stability and suppressed disorder and carrier–phonon scattering.

Speaker: Fabini, Douglas Henry (PSI - Paul Scherrer Institut)

11:50 Meissner screening at molecular phthalocyanine/superconductor interfaces probed by LE-μSR

Interfaces between a superconductor (S) and magnetic materials can host intriguing emergent states. Magnetic impurities can induce localized Yu-Shiba-Rusinov (YSR) states$^{[1]}$ that may hybridize when brought into proximity, potentially giving rise to topological superconductivity $^{[2]}$. Manganese phthalocyanine (MnPc), a spin carrying molecule with a localized magnetic moment, provides a promising platform to study magnetic interactions at the superconducting interface $^{[3]}$. Here, we investigate whether MnPc thin films can induce extended magnetic bound states in a S, as suggested previously $^{[4]}$. We employ low-energy muon spin rotation (LE-$\mu$SR) to probe the Meissner screening near the buried interface. As a first step, we study MnPc powders using bulk $\mu$SR and MnPc thin films on SiO$_2$, using ZnPc as a diamagnetic reference. We observe a gradual development of a quasi static magnetic response from the MnPc molecular spins below $10$ K on the $\mu$SR timescale. We then present preliminary LE-$\mu$SR measurements on thin films comparing MnPc/Nb and ZnPc/Nb interfaces and provide an outlook.

[1] H. Shiba, Prog. Theor. Phys. 40, 435 (1968).
[2] M. Ruby et al., Phys. Rev. Lett.115, 197204 (2015).
[3] B. W. Heinrich et al., Prog. Surf. Sci. 93, 1 (2018).
[4] S. Kezilebieke et al., Nano Lett.18, 2311 (2018).

Speaker: Ruf, Leon (Paul-Scherrer Institut, LMU)

12:10 Crystallite size-dependent local (magnetic) structures of Bi2Fe4O9 nanoparticles

The synthesis and crystallite size of a material can strongly affect its properties. Mullite-type Bi2Fe4O9 is an example of a material whose structure changes with crystallite size. Bi2Fe4O9 crystallizes in the orthorhombic space group Pbam. It undergoes a transition from a paramagnetic to an antiferromagnetic state below TN ~ 245 K. The centrosymmetric structure of Bi2Fe4O9 does not align with the reported multiferroic properties, which raises questions about the local (magnetic) structure of the material. Polyhedral distortions have been observed to increase with decreasing crystallite size, which is associated with oxygen motion. These distortions can change the spin orientation and therefore modify the local magnetic structure, leading to the observed multiferroic properties. In this work, we investigate the local (magnetic) structure of Bi2Fe4O9 nanoparticles with crystallite sizes of 35 and 400 nm using neutron total scattering and pair distribution function analysis. Reducing the crystallite size of Bi2Fe4O9 results in anisotropic unit cell expansion and a redistribution of local distortions. The magnetic structure is described with propagation vector k = (½,½,½) in a monoclinic unit cell C2/m. Modeling of the magnetic pair distribution functions measured at 100 K for both samples is needed to obtain information on the local magnetic structure.

Speaker: Nielsen, Ida (PSI - Paul Scherrer Institut)

12:30 → 13:30 Lunch @ Gartensaal

13:30 → 14:30 Panel duiscussion: Panel discussion

13:30 Staying in the Game: Risk, Reward, and keeping Curiosity in Science

Scientists today face a rapidly changing research landscape. While scientific training focuses strongly on becoming a good researcher, adaptability and resilience are becoming increasingly important.
We would like to hold an open conversation about how the scientific environment has changed across generations, what a scientific career can look like today and in the near future, and how researchers can adapt to change while remaining creative and curious. How do we stay engaged when answers become ever easier to obtain? Which skills remain uniquely valuable? And how might the relationship between experience, expertise and new technology evolve? The aim of the discussion is to explore how the nature of scientific work is changing, and what can help people build and retain fulfilling and sustainable careers in this shifting landscape.
We have assembled a diverse panel consisting of scientists from multiple career stages, with different career paths, in academia and in startup companies.

Speaker: Spitz, Leonie Christine (PSI - Paul Scherrer Institut)

14:30 → 15:00 Flash talks: Flash talks (odd)

15:00 → 16:20 Poster session: Poster session (odd/blue) with coffee @ Gartensaal

15:00 Automated Bayesian optimization of ONCV pseudopotentials

The frozen-core and pseudopotential (PSP) approximations are key to the practicality of many electronic-structure simulation methods. However, many existing methods for constructing PSP tables are labor-intensive and leave much on the table in terms of both accuracy and efficiency ("softness").

We aim to develop and disseminate automated workflows which optimize the parameters of optimized norm-conserving PSPs (ONCVPSPs), the state-of-the-art in widely-applicable (e.g. in beyond-DFT methods) yet efficient PSPs.

In our multi-fidelity, multi-objective approach, multiple physically-constrained models are trained to predict parameter feasibility and PSP softness and accuracy then used select the most promising PSP parameters to evaluate in an active-learning loop.

In preliminary optimizations of select “difficult” elements, we find that our automated Bayesian optimization can consistently find PSPs which are both more accurate and softer than the best published parameterizations.
This process generally requires 500~1000 oracle plane-wave DFT evaluations but can be completed in hours rather than the days to weeks required for manual optimization.

We are in the process of generating a full table of PBE functional PSPs to be compared to existing families (SG15, PseudoDojo, SPMS) and of extending the approach to meta-GGA functionals for which no table of PSPs is yet available.

Speaker: Zadoks, Austin Jacob (PSI - Paul Scherrer Institut)

15:00 Coherent driving of magnetoelastic dynamics in the pyrochlore spin-liquid Tb2Ti2O7

The frustrated antiferromagnet Tb2Ti2O7 is known for its strongly correlated spin-liquid ground state evading magnetic order down to 50mK. In this pyrochlore compound, the magnetic Tb3+ ions form a network of corner-sharing tetrahedra, and their crystal-field levels couple strongly to phonons, a coupling believed to help suppress magnetic order. Additionally, the material is believed to sit close to a structural instability towards a tetragonal phase. We investigate how driving lattice and orbital degrees of freedom coherently with THz pulses affects this delicate balance. Using time-resolved X-ray diffraction, we track the induced lattice dynamics and observe signatures of a transient change in lattice symmetry, while pump-induced second-harmonic generation points to a transient breaking of inversion symmetry. Supported by density functional theory, we identify the phonon and magnetoelastic modes involved. Future time-resolved X-ray magnetic linear and circular dichroism studies are anticipated to shed light on how these phonon-induced structural changes affect the magnetic state.
These results may shed new light on how lattice, spin, and orbital degrees of freedom cooperate to stabilize the spin-liquid state in Tb2Ti2O7, and demonstrate that both structural and magnetic properties can be manipulated by coherent excitation, opening new routes to control complex quantum many-body states with light.

Speaker: Spitz, Leonie Christine (PSI - Paul Scherrer Institut)

15:00 Competing quantum orders in 6R-TaS2 revealed by pressure

The transition metal dichalcogenide 6R-TaS$_{2}$ is a rich quantum platform hosting charge density wave (CDW) order, superconductivity, and an additional temperature scale at
$T^{*}\simeq40$ K marked by pronounced magnetoresistance and a nonlinear Hall effect (NHE). However, the nature of the superconducting pairing, the origin of the NHE, and their relationship with the CDW remain unclear. Using muon-spin rotation, magnetotransport and hydrostatic pressure techniques, we identify [1] a nodal superconducting state with low superfluid density at ambient pressure, with no spontaneous magnetic order detected below $T^{*}$. This rules out magnetism as the origin of the NHE. Under pressures up to 2 GPa, the superfluid density rises markedly in correlation with the superconducting transition temperature, the nodal pairing shifts to a nodeless state, and the CDW onset is reduced by half. Notably, the NHE is fully suppressed and magnetoresistance drops by 50${\%}$ within just 0.2 GPa, highlighting the fragility of the state with NHE. These results reveal competition between superconductivity, charge order, and the nonlinear Hall effect in 6R-TaS$_{2}$, driven by weakened interlayer coupling and shared electronic states.

[1] V. Sazgari et. al. and Z. Guguchia, Nature Communications 17, 5898 (2026).

Speaker: Guguchia, Zurab (PSI - Paul Scherrer Institut)

15:00 Correlated charge order intertwined with time-reversal symmetry-breaking nodal superconductivity in the dual flat band kagome superconductor CeRu3Si2

Kagome materials provide a powerful platform for exploring how flat electronic bands
promote symmetry-breaking quantum states, yet studies have so far focused mainly on
kagome-derived d-electron flat bands. In this paper, we introduce CeRu3Si2, a kagome
superconductor in which our first-principles calculations show the coexistence of Ru
d-orbital kagome flat bands and heavy-fermion flat bands derived from Ce4+ 4f-states.
X-ray diffraction reveals a dominant 1/2 charge order with a much weaker 1/3 component persisting up to room temperature. Theoretical calculations further highlight the
correlated nature of these charge-order states. Across the ARu3Si2 family (A = La, Y, and
Ce), the superconducting transition temperature Tc scales linearly with the onset temperature of normal-state TRS breaking TTRSB and the magnitude of the field-induced
magnetic response, revealing a direct positive correlation between normal-state symmetry breaking and superconductivity. Furthermore, we identify that CeRu3Si2 is the
first 132-type kagome compound to host nodal superconductivity together with spontaneous internal magnetic fields, providing clear evidence for intrinsic TRS breaking
in the superconducting state. These results establish CeRu3Si2 as a unique platform
where intertwined kagome d- and heavy fermion f-electron flat bands generate a rich
hierarchy of electronic orders.

Speaker: Gerguri, Orion (Paul Scherrer Institut)

15:00 Correlated electrons on accelerated architectures from frequency-dependent response functions

Accurately computing spectral properties of correlated quantum materials is essential for understanding many-body phenomena. However, evaluating frequency-dependent effective interactions in ab-initio simulations is computationally expensive, remaining a major bottleneck for advanced electronic-structure methods.
This project aims to implement within Quantum ESPRESSO, an open-source code for electronic-structure calculations, an efficient evaluation of dynamically screened interactions in localized manifolds using maximally localized Wannier functions (MLWFs).
Our approach integrates both a Sternheimer equation biconjugate solver and a Lanczos-Liouville formulation to compute frequency-dependent response functions within these correlated manifolds. To maximize performance and improve convergence, we also introduce divergence corrections for the Coulomb kernel and port these tools to GPU-accelerated supercomputers like Alps and LUMI.
These implementations yield major computational speed-ups in evaluating the dynamical Hubbard parameter on accelerated architectures, resolving the traditional bottleneck of calculating frequency-dependent screening. This enables highly efficient computations of Green’s functions and electronic band structures. We are currently integrating crystal symmetries to further optimize performance for complex correlated systems.
By making these calculations faster and more accessible, we aim to help the community easily explore these materials and unlock their potential for future quantum technologies.

Speaker: Dr Settembri, Paolo (PSI - Paul Scherrer Institut)

15:00 Databases of Fermi surfaces and de Haas-van Alphen oscillation frequencies from first principles simulations

The Fermi surface (FS) of a metal separates occupied from unoccupied electronic states. Knowing its shape is crucial to understanding the electronic properties of the material. Computing FS requires dense Brillouin zone sampling, and direct density functional theory (DFT) calculations are limited by computational cost. Here, we use interpolation from a basis of spatially localized projectability disentangled Wannier functions (PDWFs), a recent fully automated Wannierization algorithm [1, 2], to efficiently compute FSs for over 7'000 inorganic metals from the Materials Cloud MC3D database [3] (https://mc3d.materialscloud.org). For each FS, we compute de Haas-van Alphen frequencies, enabling direct comparison with experiments. The procedure is fully automated. In particular, based on the crystal symmetry, we determine a list of the most relevant magnetic-field rotation paths along which dHvA frequencies are computed. Simulations are orchestrated by the AiiDA workflow engine [4], ensuring FAIR data principles. Results will be made openly available in the MC3D database.

[1] J. Qiao et al., npj Comput Mater 9, 208 (2023)
[2] Y. Jiang et al., npj Comput Mater 11, 353 (2025)
[3] S. P. Huber et al., Digital Discovery, DOI: 10.1039/D5DD00415B (2026)
[4] S. P. Huber et al., Scientific data 7, 1 (2020)

Speaker: Paulish, Nataliya (PSI - Paul Scherrer Institut)

15:00 Dense rare-earth antiferromagnet coupled to microwave resonator

Strong inter-ion interactions in dense rare-earth (RE) systems such as REVO₄ and LiREF₄ can drive a phase transition to a magnetically ordered state at low temperatures. The resulting collective excitations differ fundamentally from single-ion behavior. Studying them reveals the underlying interactions and the emergent material properties they produce with relevance to quantum technology.
Here we focus on the compound LiErF4, which orders antiferromagnetically below 380 mK. The magnetic moments are coupled predominantly by dipolar interactions and undergo a quantum phase transition in an applied magnetic field. Our broadband microwave spectroscopy measurements reveal two magnon modes, one of which softens at the quantum critical point, in agreement with linear spin-wave theory.
Motivated by the proposal to use LiErF₄ for microwave-to-optical quantum transduction, we couple the material strongly to a microwave resonator, forming a polariton. Spectroscopy of this coupled system shows evidence for dielectric coupling alongside the expected magnetic coupling. In a first-of-a-kind experiment at the SwissFEL X-ray free-electron laser, we simultaneously track the antiferromagnetic order parameter to investigate the effects of domain re-formation and the quantum phase transition on the polariton. We will also discuss how this experimental setup can be extended to time-resolved measurements of polariton magnetization dynamics.

Speaker: Rutschmann, Adrian (PSI - Paul Scherrer Institut)

15:00 Density Wave Ordering with Disordered Ultracold Fermions in Optical Cavities

We investigate the interplay between cavity-induced density-wave ordering and controllable disorder in a trapped two-dimensional gas of ultracold fermions. The atoms are dispersively coupled to an optical cavity and transversely driven by a pump beam, while an additional speckle beam spatially modulates the atom-light coupling. This disorder converts the usual coupling between the cavity mode and a discrete set of density-wave Fourier components into a coupling to a continuum of fermionic density modes, weighted by the spectrum of the speckle pattern. Using linear response theory, we derive the superradiant threshold and show that the disordered interaction renormalizes the effective light-matter coupling, lowering the critical pump strength on average, with the threshold becoming self-averaging for short speckle correlation lengths. We complement this analysis with a numerical mean-field treatment that gives access to the intracavity photon number and to the real-space fermion density across the transition. These results confirm that the disorder shifts the photonic phase boundary and, above threshold, distorts the density-wave crystal by populating Fourier components beyond those selected by the clean cavity geometry. Our findings identify both the emitted cavity light and in situ density images as probes of engineered disorder in fermionic matter coupled to optical cavities.

Speaker: Rios Alves, Óscar Manuel (Paul Scherrer Institut)

Poster_thesis_A0.pdf

15:00 Effects of charge-ice correlated disorder on phonon properties

The presence of correlated disorder in materials can affect the lattice dynamics and transport properties in interesting and non-trivial ways. An example of such a material is CsNiCrF6 β-pyrochlore, in which the presence of local charge ice rules on the occupationally disordered Ni and Cr sites leads to an emergence of a loop structure, with algebraically decaying correlations. In the present work, we project the interatomic force constants obtained from DFT calculations onto a simplified model capturing the fluorine-mediated effective nearest-neighbor interaction between the disordered sites. Phonon DOS, spectra, and mode participation ratios are calculated for large realizations of the system. A selective disorder-induced broadening of the phonon spectra is observed, contrasting with the uniform broadening expected for random disorder. The mode participation ratios show partially glass-like signatures. Further work is underway to more firmly establish the link between disorder type and its signatures in phonon properties. Understanding these effects may in the future prove useful in disorder engineering of functional materials.

Speaker: Rippel, Richard (PSI)

15:00 Effects of Correlated Disorder on the Magnetic Properties of Charge Ice

Magnetic fluoride pyrochlores constitute a class of materials in which a local constraint on the arrangement of magnetic ions can lead to the formation of charge ice. These constraints generate long-range correlations throughout the system, giving rise to a particular form of disorder known as "correlated disorder", characterized by algebraically decaying spatial correlations and an emergent loop structure. This behavior contrasts with conventional uncorrelated disorder, where the introduction of a defect has only a predominantly local effect and the associated correlations decay exponentially. This project aims to investigate how correlated and uncorrelated disorder affects the thermodynamic and magnetic properties of charge ice, as well as their role in the dynamics of the system and the possible emergence of a glassy behavior.

Speaker: Willemin, Cédric Emmanuel (PSI - Paul Scherrer Institut)

15:00 Electronic properties and topological aspects of graphene nanohelicoids

We introduce graphene nanohelicoids, geometric analogues of graphene nanoribbons, in which the honeycomb lattice is embedded on a helicoidal surface. Starting from the three-dimensional helical structure, we construct effective one-dimensional lattice models with band structures characterized by a momentum-shifted particle–hole relation $E_v(k)=-E_c(k+\pi)$ that reflects an anti-chiral symmetry arising from the nonsymmorphic symmetry. A systematic investigation of graphene nanohelicoids using the tight-binding approximation reveals a number of trends upon varying width and edge orientation, for instance, alternating transitions between semiconducting and metallic regimes. As the structure width varies, the band gap periodically closes and reopens, accompanied by an alternating Zak phase that switches between trivial and nontrivial. Using an analytic tight-binding model with a continuous deformation of the graphene nanohelicoids, we explain the origin of width- and termination-dependent band inversion and alternating Zak phase, and derive the relationship between the termination-resolved index and the sublattice symmetry operator in one-dimensional nonsymmorphic systems.

Speaker: Herasymchuk, Arsen (Paul Scherrer Institute PSI)

15:00 Extending Magnetic Racetrack Devices into Three Dimensions Using Freestanding Membranes

For next-generation spintronic memory and logic devices, three-dimensional (3D) integration offers new opportunities because of the increased device density and new functionalities that are inaccessible in conventional planar spintronics. The transfer of freestanding magnetic membranes onto surfaces with predefined geometries offers a versatile route towards such 3D integration by decoupling the growth of high-quality magnetic heterostructures from the fabrication of the underlying 3D structures.

Building on our previous demonstration of 3D magnetic racetrack memory using freestanding membranes [1], we are extending this approach towards more complex 3D spintronic devices. In particular, we are exploring the integration of racetrack devices with high-aspect-ratio 3D geometries, with the aim of extending established concepts of domain-wall logic beyond conventional planar architectures [2]. These 3D racetrack architectures could provide new possibilities for controlling domain-wall propagation and integrating memory and logic functionalities within the same compact platform.

[1] K. Gu et al., Nature Nanotechnology 17, 1065–1071 (2022).
[2] Z. Luo et al., Nature 579, 214–218 (2020).

Speaker: Gu, Ke (1. Laboratory for Mesoscopic Systems, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland 2. PSI Center for Neutron and Muon Sciences, 5232 Villigen PSI, Switzerland)

15:00 Ferroelectric domains imaged by X-ray linear dichroism ptychography

The rapid development of modern information technologies in the artificial intelligence era is increasing demand for materials that enable high information density, fast operation, and low energy consumption in data processing and storage. Non-volatile ferroelectric materials are promising candidates because they can integrate data processing and storage within a single unit, potentially reducing energy consumption while increasing operation speed. Realizing this potential requires a detailed understanding of the nanoscale mechanisms governing their functional response. In particular, a key step is to image the domains and domain walls and connect their structure to the ferroelectric properties. Although surface-sensitive techniques such as piezoresponse force microscopy and second-harmonic generation microscopy have been successfully imaged ferroelectric thin films, three-dimensional domain imaging remains underexplored. Such imaging is essential for distinguishing intrinsic bulk polarization patterns from surface-induced effects.

Here, we use both soft- and hard-X-ray ptychography to image ferroelectric domains in single-crystal BaTiO$_3$ and polycrystalline PbZr$_{0.52}$Ti$_{0.48}$O$_3$. Leveraging X-ray linear dichroism in both energy ranges, we obtained high-spatial-resolution images with clear domain contrast. Energy-dependent measurements reveal a strong dichroic signal in both absorption and phase. The imaging of ferroelectric domains with synchrotron X-ray ptychography is a first important step toward three-dimensional tomographic imaging of ferroelectric domain structures.

Speaker: Li, Jingwen (PSI - ETH Zurich)

15:00 First principles treatment of ARPES matrix element simulations via Kohn-Sham scattering states

Angle-resolved photoemission spectroscopy (ARPES) offers direct insight into electronic structure, with the measured intensity determined by both the single-particle spectral function and the photoemission matrix element. While the spectral function captures intrinsic many-body properties, matrix-element effects can strongly modify the observed intensity depending on photon energy, polarization, and experimental geometry, complicating spectral interpretation. At the same time, these effects provide access to the quantum geometry of electronic states, including orbital angular momentum and Berry curvature, which are relevant to topological phenomena and orbitronic applications.

Accurate and efficient treatment of photoemission matrix elements therefore requires a reliable description of the photoelectron final state. Here, we obtain the final state by solving the Kohn-Sham scattering problem in an ARPES geometry with time-reversed low-energy electron diffraction (trLEED) boundary conditions. We benchmark the approach against experimental circular-dichroism ARPES data at multiple photon energies and find excellent agreement. Our framework provides a practical route to incorporating matrix-element effects into ARPES simulations, enabling more reliable extraction of intrinsic electronic and topological properties and providing a basis for ab initio simulations of pump-probe time-resolved ARPES.

Speaker: Parusa, Gian (PSI - Paul Scherrer Institut)

PSI_CMR2026_poster_Parusa.pdf

15:00 Growth and magnetic characterization of ilmenite-type complex oxides

Ilmenite-type hexagonal ABO₃ oxides are a class of honeycomb-layered antiferromagnetic insulators that display a wide variety of exotic physics, ranging from magnetoelectricity and ferrotoroidicity to topological magnons and spin liquid candidates.
Previous research has focused mostly on bulk samples of these compounds, while only a few studies have been performed on thin films. We aim to investigate the effects of strain, lattice, and heterostructure engineering on the functional properties of ilmenite thin films, using pulsed laser deposition on a selection of substrates.
We have currently established a broad growth window for high-quality epitaxial thin films of both magnetoelectric MnTiO₃ and spin liquid candidate CoTiO₃ on Al2O₃ and characterized their structural properties with XRD and AFM. X-ray reciprocal space mapping and SQUID magnetometry will be used to relate the epitaxial strain state to the magnetic properties in our films. These measurements will provide a basis for exploring further advanced characterization such as XLD/XMCD or μSR.
Our work towards epitaxial tuning of functional properties in ilmenite thin films may reveal a promising new platform for complex oxide materials alongside the more established perovskite ABO₃ systems.

Speaker: Duncan, Benjamin Bryan (University of Zurich)

2026_PSI_CondensedMatterRetreat_Poster_Benjamin_v2.pdf

15:00 Hidden chiral signatures in ferroaxial K2Zr(PO4)2

Ferroaxial order is a ferroic order that preserves time-reversal and spatial inversion
symmetry and thus is unaffected by depolarizing electric or magnetic fields. From a symmetry perspective, purely ferroaxial
materials serve as a suitable platform for studying hidden chiral properties as structural
chirality can be induced in them by breaking inversion symmetry.
In this work, we use first-principles calculations and multipole analyses to investigate the
relationship between ferroaxiality and chirality in both real and momentum space
focusing on the prototypical ferroaxial material K2Zr(PO4)2 [1]. We demonstrate that
while the paraxial phase of K2Zr(PO4)2 is non-chiral, the ferroaxial phase is antiferro-
chiral, using the local electric toroidal monopole as measure of electronic chirality [2].
We show that applying an electric field induces ferri-chiral order with net electronic
chirality that is opposite for opposite underlying ferroaxial domains and can be
manipulated by the strength and direction of the electric field. Associated with the
induced chirality in real space we find non-zero components in the Berry curvature dipole
tensor that switch sign between opposite ferri-chiral domains.

[1] N. Taufertshöfer, A. Narayan, and N. A. Spaldin arXiv:2607.29573
[2] R. Oiwa and H. Kusunose Phys. Rev. Lett. 129, 116401 (2022)

Speaker: Taufertshöfer, Nora (Materials Theory, ETH Zürich)

15:00 High-Pressure Phase Transition Mechanisms in Gd₂Zr₂O₇

Gd₂Zr₂O₇ (GZO) is an advanced radiation-resistant ceramic whose structural response to pressure is relevant to understanding its stability and transformation behaviour under irradiation. Its high-pressure phase is difficult to characterise because substantial local disorder limits conventional crystallographic refinement.
This work investigates the pyrochlore-to-defect-cotunnite transition in GZO by combining atomistic modelling, experimental pair distribution functions (PDFs), energetics, and transition mechanisms.
First-principles and machine-learning-potential calculations were used to explore oxygen configurations and cation arrangements in defect-cotunnite GZO and to assess their pressure-dependent stability. Candidate structures and disorder models were compared with high-pressure PDF measurements, while three physically motivated transition mechanisms were investigated, including concerted distortion, cation-plane shearing, and close-packed-plane sliding.
The calculations show that oxygen site preference changes with pressure, with tetrahedral sites favoured at low pressure and octahedral occupancy becoming favourable upon compression. Although a metastable structure provides an improved PDF fit, its refined Zr displacement parameter is unphysically small, motivating the exploration of alternative Gd–Zr arrangements. Molecular-dynamics simulations provide evidence that compact cation-plane sliding can mediate the structural transformation.
The results highlight how physically motivated transition mechanisms and first-principles calculations can guide structural modelling when local-structure data cannot be interpreted using conventional structure determination tools.

Speaker: Mr Tettamanti, Pietro (Paul Scherrer Institute)

GZO_HP_Mech_poster_A0.pdf

15:00 Hybridization-driven orbital anisotropy in CrSBr

CrSBr is a 2D van der Waals material [1]. It is a fascinating system exhibiting quasi-1D properties as evidenced by several probes, such as ARPES [2], transport [3] and STM [4]. It orders antiferromagnetically below TN =132 K. Monolayer CrSBr is ferromagnetic with Tc =146K [5]. In this work, we have investigated the large in-plane orbital anisotropy of CrSBr by measuring x-ray linear dichroism at the Cr L3,2-edges in combination with ab-initio simulations [6]. A large XLD persists above TN. Our simulations show that the orbitals along b-axis are occupied, in agreement with previous predictions [4]. In addition, the large XLD is reproduced only when the hybridization of Cr with its ligands is included in the theoretical description using Wannier orbitals.

[1] E. J. Telford et al., Advanced Materials 32, 2003240 (2020).
[2] S. Smolenski et al., Nat Commun 16, 1134 (2025).
[3] F. Wu et al., Advanced Materials 34, 2109759 (2022).
[4] J. Klein et al., ACS Nano 1 (2023).
[5] Lee et al., Nano Lett. 21, 3511 (2021).
[6] C. Piamonteze, C. Cardot D. HovancIk, G. T. Seidler, J. J. Kas, J. J. Rehr, N. Machacova, V. Sechovsky, J. Pospisil, and K. Carva, in preparation

Speaker: Piamonteze, Cinthia (PSI - Paul Scherrer Institut)

15:00 Isotropic spin-orbit coupling drives nodal-line superconductivity in chiral LaIrSi

Structural handedness is a defining characteristic of chiral crystals, which are known to exhibit exotic quantum phenomena resulting from the interaction of band topology, spin-orbit coupling (SOC) and electronic correlations. Yet, their potential for unconventional superconductivity (SC) remains largely unexplored due to the scarcity of suitable materials. Here, we investigate the origin of unconventional SC in the chiral La(Rh,Ir)Si family, a double-helix system hosting multifold fermions absent in other topological chiral crystals. Combining muon-spin spectroscopy, band-structure calculations, and perturbation theory, we probe how substituting 4d-Rh with 5d-Ir reshapes the superconducting gap structure. This substitution significantly enhances SOC, driving a transition from fully-gapped SC in LaRhSi to topological nodal-line SC in LaIrSi. Our theoretical model shows that this nodal-line state arises from isotropic SOC of a specific strength — challenging the established view that unconventional SC requires strongly anisotropic SOC to stabilize triplet pairing. Our results establish a new phase diagram linking SOC strength and symmetry to pairing structure, providing a comprehensive roadmap for identifying and engineering unconventional superconductivity in chiral crystals.

1. P. Narang, C. Garcia, and C. Felser, Nat. Mater. 20, 293 (2021).
2. T. Shang et al., T. Shiroka, Adv. Mater. 37, e11385 (2025).

Speaker: Shiroka, Toni (PSI - Paul Scherrer Institut)

15:00 Leveraging generative AI to reconstruct unknown positions of hydrogen sites

Generative AI methods are rapidly evolving to speed up and improve materials discovery. Diffusion based models can not only be adopted to generate new materials with desired properties but also to reconstruct crystal structures for which structural information is only partially available [2]. In this work, we use Microsoft’s mattergen [1], a diffusion based model originally designed to generate new stable crystal structures, and apply it to reconstruct missing hydrogen sites in crystal structures reported in experimental databases. This is particularly useful as the experimental measurement of hydrogen sites with standard XRD is typically challenging due to weak scattering of hydrogen. We show how to leverage approaches known from image inpainting in the field of computer vision, combined with universal machine learning interatomic potentials, to improve the success rate of correctly identifying the missing sites while significantly lowering the computational cost with respect to a direct DFT approach.

[1] Zeni, C. et al., Nature 639, 624–632 (2025)
[2] Zhong, P. et al., arXiv:2504.16893v1 (2025)

Speaker: Reents, Timo (PSI - Paul Scherrer Institut)

15:00 Magnetic ground state and excitations of ErVO4

Rare-earth insulators such as LiHoF$_4$ and LiErF$_4$ are model systems for quantum magnetism, where dipolar interactions, crystal fields and quantum criticality compete. LiErF$_4$ was recently proposed as a microwave-to-optical quantum transducer, a component necessary to realize future quantum networks.

Here, we investigate the largely unexplored material ErVO$_4$ by determining its magnetic ground state and excitations, for which we combine specific heat capacity and magnetization measurements with microwave spectroscopy and neutron diffraction. Our magnetic structure refinement establishes that magnetism sets in below $T_{\rm N} ≈350$ mK and adopts a bilayer antiferromagnetic structure akin LiErF$_4$, with moments in the basal plane almost parallel to the crystallographic b axis. Field-temperature phase diagrams for H || a and H || c identify quantum phase transitions to a field-polarized phase. Microwave spectroscopy reveals a zero-wavevector magnon mode that deviates from purely dipolar predictions, pointing to the presence of additional interactions.

Forthcoming, we plan to measure the spin wave dispersion by inelastic neutron scattering to pin down the exchange and magneto-elastic couplings, which will provide a basis to establish the suitability of the material for microwave-to-optical quantum transduction.

Speaker: Kazarian, Karina (PSI - Paul Scherrer Institut)

15:00 Magnetic structure, electronic and charge-lattice modulationsin in superconducting Ruddlesden-Popper nickelates

Pressure-induced high-temperature superconductivity (HTS), with an onset Tc as high as 96 K, has been recently discovered in Ruddlesden-Popper nickelates. This has made La3Ni2O7 a central system for determining how spin, charge, and lattice degrees of freedom contribute to superconductivity. Ongoing studies aim to map out spin density wave (SDW), charge density wave (CDW), and superconducting phases across different compositions and structural motifs. By tailoring the chemical composition and tuning structural features through external parameters such as temperature and pressure, it becomes possible to influence the balance between these competing ordering phenomena.
We present the current understanding of DW transitions in La3Ni2O7-family with particular emphasis on the role of chemical substitution influence over the structural transformations and the evolution of SDW, CDW, and superconducting phases. We address future directions that may help uncover the mechanisms driving superconductivity in these complex oxide systems. The exploration of novel chemical variants and their associated magnetic structures is outlined together with current limitations in synthesis and characterization, with the goal of clarifying the superconductivity mechanisms and their interplay with competing orders.

Speaker: Plekhanov, Maksim (Paul Scherrer Institute)

15:00 Mapping the configuration of thick permanent magnets with pre-edge hard X-ray magnetic tomography

In recent years, there has been growing interest in three-dimensional, unconfined magnetic systems, due to the prospect for complex magnetic configurations in the bulk, with application-relevant behaviour.
Until now, imaging of magnetic systems has been limited to samples of a few micrometres in size, while thicker systems have only been studied using surface-sensitive techniques. However, thinning magnetic materials changes the magnetic behaviour, so imaging at the nanoscale in system-representative samples is necessary. Here, we demonstrate transmission imaging of magnetic samples up to 50 µm thick, an order of magnitude thicker than previously possible. We used spectroscopic hard X-ray magnetic circular dichroism to image Nd2Fe14B, one of the most widely used permanent magnets. For thicknesses above 30 µm, we observed surface-localised domains, previously observed in surface-sensitive optical measurements of similar samples. By tilting the sample, we demonstrated that these domain structures vary through the thickness, rather than forming a single domain. We exploited dual-axis magnetic tomography for the first 3D imaging of magnets thicker than 5 µm. We demonstrate how pre-edge hard X-ray magnetic imaging can reveal the internal nanoscale magnetic configuration of truly bulk systems.

Speaker: Lautizi, Ginevra

15:00 MC3D: The Materials Cloud FAIR and full-provenance materials database

We introduce MC3D, the Materials Cloud database of ab initio calculated properties of experimentally synthesized materials. Structures were extracted from the Pauling File, ICSD, and COD, resulting in 72,609 unique stoichiometric inorganic compounds curated and refined using DFT at the PBEsol level, employing as quantum engine the community-developed open-source Quantum ESPRESSO and the SIRIUS library for efficient use of GPU hardware. All simulations are managed by AiiDA, ensuring complete data provenance, reproducibility, and workflow automation. MC3D is openly accessible via the Materials Cloud platform (https://mc3d.materialscloud.org). This resource is designed to support applications ranging from machine learning to high-throughput studies, offering a robust, transparent foundation for materials discovery. We will demonstrate our protocols, validation, and AiiDA's automation and error-handling features, which create robust workflows for electronic structure simulations, along with current applications of the database.

Speaker: Minotakis, Michail (PSI - Paul Scherrer Institut)

mc3d_poster.pptx.pdf

15:00 Momentum-resolved low-energy excitations in the kagome semimetal Ni3In2S2

Kagome materials host characteristic electronic structures, including flat bands and topological band crossings. Here, we investigate the kagome semimetal Ni3In2S2 using resonant inelastic X-ray scattering (RIXS). By tuning the incident energy across the Ni L3 edge and measuring spectra along the Γ-M direction, we identify a broad excitation centered near 0.6 eV. Its spectral weight is strongly enhanced near Γ and progressively suppressed toward M, indicating a highly momentum-selective electronic excitation. This momentum dependence resembles that of the flat-band-related Stoner excitation observed in ferromagnetic Co3Sn2S2. Comparing nonmagnetic Ni3In2S2 with magnetic Co3Sn2S2 enables us to distinguish the influence of the kagome band structure from that of magnetism on these itinerant electronic excitations.

Speaker: Tao, Zhen (PSI - Paul Scherrer Institut)

15:00 Optimizing the applications of track reconstruction in μSR measurements - High pressure and microscale resolution

Monolithic silicon pixel detectors open new possibilities for $\mu$SR-based experiments by enabling spatial resolution through the reconstruction of incoming $\mu^+$ and decay $e^+$ trajectories. We present Geant4-based musrSim studies of two applications. The first aims to enable $\mu$SR under high hydrostatic pressure using diamond anvil cells, reaching up to ten times higher pressure than standard piston-cylinder cells. We optimize the cell alignment with respect to the beam to maximize the fraction of muons stopping in the sample. The second concerns low-energy $\mu$SR, where reconstructing the $e^+$ trajectory provides lateral resolution at the micron scale, enabling studies of novel devices.

Speaker: Mirbaghestan, Kimia

15:00 Probing Effects of Non-Magnetic Zn Impurities on the Spin Stripe Order in La2-xSrxNiO4 by muSR Spectroscopy

Muon spin rotation (muSR) results of Zn doping (0−12%) on the stripe ordered phase in La$_{2-x}$Sr$_x$NiO$_4$ ($x$ = 1/3) are presented. Zero field (ZF) and weak transverse field (wTF) experiments of high-quality polycrystalline samples are used to determine the magnetic transition temperature, the magnetically ordered volume, the internal field and relaxation rates. With these results, a phase diagram under doping with nonmagnetic Zn impurities is constructed and put in context with related cuprates. A strong, non-monotonic dependence of the spin ordering temperature on the Zn content is detected and two regimes of suppression of magnetic order are identified.
Firstly, at low Zn doping, a fast linear reduction is present which is reminiscent of the behavior in cuprates. This can be linked to the disruption of stripe order by non-magnetic impurities.
Secondly, at high doping, slow suppression of spin order occurs and is related to the dilution of the magnetic structure with non-magnetic impurity atoms. Extrapolation suggest a critical doping for this regime close to the percolation threshold.
Understanding the effects of non-magnetic impurities on the stripe-ordered phase in La$_{2–x}$Sr$_x$NiO$_4$ can provide valuable insights into the interplay between superconductivity and stripe order in related nickelate and cuprate superconductors.

Speaker: Spitaler, Maximilian (PSI)

15:00 Research activities at the Materials Discovery Laboratory

Materials Discovery Laboratory is a synthesis and crystal growth facility within the Department of Materials at ETH Zurich. Its research spans Materials Science, Solid State Chemistry and Condensed Matter Physics, focusing on the study of materials exhibiting exotic states of matter (e.g., topological insulators, superconductors, and skyrmion lattices), frustrated magnetism (e.g., pyrochlores and garnets), multiferroic, ferroelectric and magnetoelectric properties, as well as 2D magnetism. The laboratory’s infrastructure enables the preparation of polycrystalline and single crystal samples of a wide range of inorganic compounds, including as oxides, borides, chalcogenides, oxichalcogenides and intermetallics. I will present key capabilities of this facility and highlight the scientific advances it has enabled across several emerging research areas.

Speaker: Dr Ciomaga Hatnean, Monica (PSI - Paul Scherrer Institut)

15:00 Scattering of visible light from the quantum ferromagnet LiHoF4

LiHoF$_4$ is an experimental realization of the transverse-field Ising model with dipolar ferromagnetic order that is suppressed by a transverse magnetic field at $\mu_0H_{\rm c} = 5.1$ T. At low temperatures, hyperfine coupling to the Ho nuclear spins further stabilizes the ordered phase and softens the coupled electronic-nuclear modes near the quantum critical point.
Beyond this microscopic description, LiHoF$_4$ also forms mesoscopic magnetic domains. AC susceptibility measurements reveal an interplay between the mesoscale domain physics and the underlying microscopic quantum Hamiltonian. However, these experiments do not provide direct evidence of the magnetic domain and domain-wall structure.
Our visible-light scattering measurements performed at sub-Kelvin temperatures provide a strong magnetic signal from the ferromagnetic domains of LiHoF$_4$. A transverse field-induced conversion of a random speckle pattern to a sharp crystal-like diffraction pattern directly images the domain wall depinning inferred from the AC susceptibility results, as well as a line of quantum critical points from a well-organized domain state. Curiously, there are also unexpected features of the transverse-field response, including an angular offset between the applied transverse field and the diffraction pattern that points to the importance of magneto-elastic interactions, as well as oscillations observed in the Bragg-peak intensities.

Speaker: Clémence, Maël (PSI - Paul Scherrer Institut)

15:00 Soft-X-ray ARPES: From fundamental science to devices

Angle-resolved photoelectron spectroscopy (ARPES) resolves fundamental properties of solid-state systems – electron dispersions, Fermi surfaces, electron-boson coupling – in electron momentum k. Extending ARPES to soft-X-ray energies around 1 keV provides large probing depth, sharp definition of three-dimensional k, and chemical-state-specific resonant photoexcitation. These capabilities make this technique particularly suited to buried interfaces, heterostructures and impurity systems relevant to electronic and quantum devices.
Our application examples include Ga₂O₃, a paradigm ultrawide-bandgap semiconductor, where we determine the VBM location in three-dimensional k-space, with direct implications for its optical properties. At GaN/AlN interfaces, we explore electron dispersions and Fermi surfaces of electron and hole gases relevant to n- and p-channel high-electron-mobility transistors. At buried NbN/GaN interfaces, we explore k-dependent coupling of NbN superconducting states into GaN for quantum-device integration. Another example is electronic states in phosphorus and arsenic δ-layers in Si for quantum-dot devices. In complex oxides, we trace the evolution of charge-carrier mobility from heavy Ti 3d-derived polaronic charge carriers at the LaAlO₃/SrTiO₃ paradigm interface to anomalous band ordering in SrTiO₃-based systems and finally to highly mobile, lattice-decoupled Sn 4s-derived carriers in BaSnO₃.
These results demonstrate the growing role of soft-X-ray ARPES in understanding and engineering novel electronic and quantum materials.

Speaker: Strocov, Vladimir N. (PSI)

15:00 Sputtering Options at the LIN neutron optics facilities

Our sputtering lab provides their coating services for all PSI groups and produces neutron optical coatings (supermirrors).
We are collaborating with all PSI large-scale structures for instrumentation devices and sample production.
The lab is equipped with 2 sputtering plants that have 3 target stations each and cover 50x200 mm^2 and 400 x 580 mm^2 respectively. Both DC magnetron and RF-sputtering are possible, including reactive sputtering. Sample heating is available.
A recent addition is a UHV deposition chamber that allows in-situ neutron measurements during the deposition. 3 sputter guns (magnetron DC, RF) are available. The equipment has been already used on a neutron reflectometer.
We would like to push the development of supermirrors further and would benefit from additional expertise in thin layer characterization.
While specialized in multilayer production with a keen interest in neutron supermirror development, we are open to collaborate in other scientific domains, in particular in relation to neutrons.

Speaker: Klauser, Christine (PSI - Paul Scherrer Institut)

15:00 Toward control of magnetism by coherent chiral acoustic phonons

Coherent acoustic phonons can carry not only energy and linear momentum but also in some cases angular momentum. We aim to study using optical and x-ray scattering techniques the question of how chiral phonons can be generated and detected in non-centrosymmetric materials, and how it might be able to couple to magnetic order. Existing optical data shows the creation of transverse modes that are predicted to carry angular momentum. Future work includes time-resolved x-ray scattering to experimentally measure the angular momentum and time-resolved magneto-optic measurements to measure possible coupling to magnetism in metallic films.

Speaker: Johnson, Steven (PSI - Paul Scherrer Institut)

15:00 Ultrafast switching of GdCo nanomagnet arrays

Nanomagnet arrays can provide alternative cost-efficient systems to compute and store information [1,2]. A main target of current research is to achieve a reliable and fast manipulation of their states.
In recent experiments [3,4], it was shown that ultrafast reorientation of macrospins associated with the nanomagnets in artificial spin ices (ASI) can be achieved, with the nanomagnets arranged on square and Kagome lattices. However, although multiple laser pulses are required to achieve control over large areas.
We show how to achieve, through a single laser pulse, reliable, large-area switching of macrospins for various GdCo nanomagnet arrays. The phenomenon is fluence- and polarization-dependent. Combining the laser pulses with writing the initial magnetic configuration with a magnetic force microscope (MFM) tip, we aim to achieve an advanced control of complex nanomagnet arrays.

[1] A. Imre et al., Science 311, 5758 (2006)
[2] H. Arava et al., Nanotechnology 29, 265205 (2018)
[3] D. Pecchio et al., Phys. Rev. B 113, 064404 (2026)
[4] D. Pecchio et al., Phys. Rev. B 113, 054434 (2026)

Speaker: Soranzio, Davide (1. Laboratory for Mesoscopic Systems, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland 2. PSI Center for Neutron and Muon Sciences, 5232 Villigen PSI, Switzerland)

15:00 Unraveling density-wave (DW) order in superconducting nickelates via nuclear magnetic resonance (NMR)

The discovery of superconductivity in pressurized Ruddlesden-Popper nickelates, such as La₃Ni₂O₇, has sparked intense interest. Superconductivity emerges upon suppression of an ambient-pressure DW order, drawing striking parallels with the cuprates

While muon spectroscopy probes the well-known spin density wave (SDW), it cannot detect charge order. Clarifying this intertwined CDW via NMR is essential to understand the pairing mechanism.

NMR measurements at 5.0 T on a polycrystalline La₃Ni₂O₇ sample, track the temperature evolution of the longitudinal relaxation rate (T1) from 77 K to room temperature. A peak in (T₁T)⁻¹ near 153 K, signal SDW transition, together with a distinct slope change near 140 K that we attribute to the CDW instability.

Our findings establish a baseline for forthcoming high-pressure NMR studies and motivate our ongoing investigation of Pr-doped La₃Ni₂O₇, aimed at tracking the key order parameters across the phase diagram and uncovering further DW transitions.

Speaker: Valenti, Diego (PSI - Paul Scherrer Institut)

16:20 → 17:20 Contributed talks: Session 6

Convener: Guguchia, Zurab (PSI - Paul Scherrer Institut)

16:20 Layered perovskites: from epitaxy to chemical property tuning

Layered perovskite-based compounds offer a range of functional properties enabled by their naturally anisotropic structure [1]. This provides opportunities to combine electrical conductivity, ferroelectricity and magnetic order in ways that are difficult to achieve in conventional perovskites.

In this talk, I will present our work on epitaxial thin films of the Aurivillius and Carpy–Galy families, taking $\mathrm{Bi_5FeTi_3O_{15}}$ [2] and $\mathrm{La_2Ti_2O_7}$ [3] as examples. Using pulsed laser deposition, we stabilize these layered phases on suitable single-crystal substrates. We demonstrate in-plane ferroelectricity down to a single unit cell and show how these materials can control interfacial electrostatics in oxide heterostructures. I will also discuss how post-growth redox reactions can chemically modify their electronic properties, opening routes towards polar metallicity in layered ferroelectrics.

These results will introduce the directions we aim to develop in our new Solid-State Materials Chemistry group at ETH Zurich, combining epitaxial growth and chemical transformations to explore the coexistence and coupling of different functional properties.

[1] E. Gradauskaite, Small Sci. 6, e202500488 (2026).
[2] E. Gradauskaite et al., Nat. Mater. 22, 1492–1498 (2023).
[3] E. Gradauskaite et al., Adv. Mater. 37, 2416963 (2025).

Speaker: Gradauskaite, Elzbieta (ETH Zurich)

16:40 Spectroscopic studies on freestanding transition metal oxides films

Freestanding oxide films provide a platform to explore materials physics in the quasi-two-dimensional limit, where the influence of a supporting substrate is strongly reduced. These films also enable X-ray spectroscopy experiments in geometries that are not accessible with bulk samples.
In this presentation, I will discuss how X-ray diffraction and complementary spectroscopies can reveal structural and electronic changes in freestanding transition-metal oxides (TMOs).
We combine X-ray diffraction and X-ray absorption, linear and circular dichroism, resonant emission, and resonant inelastic X-ray scattering to investigate the interplay between lattice and electronic degrees of freedom. Using freestanding SrTiO films as model systems, we track structural distortions and electronic excitations as a function of thickness and temperature.
Our results demonstrate that reducing the dimensionality can modify structural instabilities, electronic states, and collective excitations compared with their bulk counterparts. Remarkably, freestanding films exhibit properties distinct from bulk materials and strained epitaxial-grown films.
These studies establish freestanding oxide films as a versatile platform for discovering and controlling emergent quantum states, while opening new opportunities for in-situ X-ray studies of functional materials.

Speaker: Huang, Shih-Wen (PSI - Paul Scherrer Institut)

17:00 AI-driven autonomous workflow for PLD growth with in-situ RHEED

Pulsed laser deposition (PLD) is a physical vapor deposition technique known for its versatility, as well as for its complexity. The growth of a novel material requires multidimensional optimization to finely tune the synthesis parameters. This procedure typically relies on inefficient trial-and-error approaches. Consequently, developing systems that autonomously drive an efficient exploration of the parameter space can accelerate the synthesis of desired thin films.
In this work, we demonstrate the implementation of a growth-mode-based metric as the key driver for autonomous parameter optimization in PLD. Using in situ reflection high-energy electron diffraction (RHEED) and extending existing machine-learning algorithms, we developed an automated, machine-learning-based analysis to evaluate deposition quality and identify the growth regime. Starting from raw RHEED videos we compute a scalar value which quantifies how closely the growth approximates an ideal layer-by-layer mode. By feeding this RHEED-based metric into a Bayesian optimization workflow, the algorithm iteratively suggests new sets of parameters driving an efficient exploration of the parameter space. We demonstrate the optimized layer-by-layer growth of Ag(Nb,Ta)O3 (ANT) films achieved in less than 15 depositions and driven by autonomous parameter selection based on our custom-designed RHEED metric. This workflow is the first step en route to autonomous PLD laboratories.

Speaker: Mani, Pietro (PSI - Paul Scherrer Institut)

17:20 → 18:00 Closing: Closing session

Convener: Gerber, Simon (PSI - Paul Scherrer Institut)

17:20 Closing remarks - Gabriel Aeppli

Speaker: Aeppli, Gabriel (PSI - Paul Scherrer Institut)

17:40 Closing remarks - Marc Janoschek

Speaker: Janoschek, Marc (PSI - Paul Scherrer Institut)