Toward first principle approaches to X-ray spectroscopies

by Mr Yun Yen (PSI/LMS)

Thursday 13 Jun 2024, 15:00 → 16:00 Europe/Zurich

OVGA/200

Photon-based spectroscopies such as angle-resolved photoemission spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) are some of the most powerful tools to study the electronic properties of quantum materials. ARPES can be used to access the quasiparticle electronic band structure, or extract aspects of the Bloch wave-functions by exploiting the polarization degree of freedom such as circular dichroism ARPES (CD-ARPES). I will first briefly discuss the Wannier-function methodology for ARPES simulation, which allows us to compute photoemission matrix elements.  XAS and RIXS, on the other hand, can be used to reveal magnetic properties of correlated materials, including their corresponding magnetic or orbital excitations. I will discuss our workflow for simulating such core-level spectroscopies. From ab-initio Wannier tight binding parameters and constrained random phase approximation (cRPA), we construct a correlated atomic model Hamiltonian with effective hybridization, crystal field, and Coulomb interaction tensor, and calculate the spectrum with exact diagonalization. As an illustration, I will show the simulation of the multiferroic material YBaCuFeO₅, where we track the signature of spin spiral ordering in the RIXS spectrum.