Condensed Matter Physics in the Alps: Geometric Frustration, Topology, Flat Bands, and Correlation in Kagome and Van der Waals Systems

Revealing Correlations and Orbital Textures in Quantum Materials with photoemission spectroscopy

6 Jan 2026, 10:15

35m

Saas Fee

Invited talk (by invitation only) Theory Tuesday Morning Session II, Chair A. Imamoglu

Speaker

Michael Schüler (Paul Scherrer Institute)

Description

Angle-resolved photoemission spectroscopy (ARPES) provides direct momentum-resolved access to correlation effects and orbital textures in quantum materials. In this talk, I will show how a combined experimental and theoretical approach allows us to extract these key electronic properties in van der Waals and Kagome-related systems.

First, I will discuss our ARPES and dynamical-mean-field-theory analysis of Nb₃Br₈ [1]. By mapping the out-of-plane dispersion, we identify a clear momentum-space fingerprint of a dimerized Mott insulator—namely a 2π/d periodicity of the valence-band maxima—demonstrating how correlations reshape the spectral function of a weakly dimerized layered material.

Second, I will present how circular-dichroism ARPES, supported by first-principles and Wannier-based photoemission simulations, reveals monopole-like orbital angular momentum (OAM) textures in chiral topological semimetals such as PtGa and PdGa [2]. The ability to reverse the monopole polarity by switching structural chirality highlights new routes for controlling orbital polarization.
Together, these results illustrate how ARPES, in synergy with advanced modeling, can uncover both correlation-driven physics and complex OAM textures, offering new opportunities for designing correlated and orbitronic quantum materials.

[1] Date et al., Momentum-resolved fingerprint of Mottness in layer-dimerized Nb3Br8 Nat Commun 16 4037 (2025)
[2] Yen et al., Controllable orbital angular momentum monopoles in chiral topological semimetals Nat. Phys. 20 1912 (2024)