Advancing Theoretical Methods for Photon-Based Spectroscopies in Quantum Materials

by Mr Yun Yen (PSI/LMS)

Wednesday 3 Sept 2025, 15:00 → 16:00 Europe/Zurich

WBGB/019

Quantum materials exhibit exotic properties and intriguing collective phenomena arising from quantum degrees of freedom and strong many-body correlations, offering significant potential for novel technological applications. Photon-based spectroscopies, including angle-resolved photoemission spectroscopy (ARPES) and resonant inelastic X-ray spectroscopy (RIXS), have become essential tools for investigating these properties both in equilibrium and out-of-equilibrium. 

In this public defense, I will present part of my thesis, which focuses on developing theoretical methods for photon-based spectroscopies. First, I introduce the Wannier-ARPES formalism for calculating photoemission matrix elements using Wannier-based tight-binding models. A key result is a microscopic theory of circular dichroism in ARPES (CD-ARPES), enabling access to wavefunction properties like orbital textures and band topology. The second part focuses on ultrafast dynamics in time-resolved ARPES  (tr-ARPES), especially in the context of Floquet engineering. I will briefly discuss signatures of non-adiabatic dynamics between Floquet states in nonlinear photoemission, offering insights into strong-field-driven phenomena and the development of ultrafast lightwave electronics.