Title: Ab Initio Many-Body Physics in Light-Driven Quantum Materials

Abstract: Light-matter interaction is of particular importance in quantum systems, which is central to technological applications such as optoelectronics, spin-current generation, and artificial photosynthesis. It is also rooted in many fundamental physical processes, including creating and manipulating emergent quasiparticles, engineering topological phases, and cavity electrodynamics, enabling a plethora of experimental spectroscopies for the detection of exotic phases and behaviors under extreme conditions. The lattice vibrations in quantum materials, and the incurred electron-phonon coupling, are among those factors that make the manifestations of light-matter interaction so versatile, and in this talk, I will discuss two consequences of light-matter interaction in systems with vibrational degrees of freedom, from the perspective of ab initio many-body perturbation theory. First, I will focus on continuous light illumination and discuss our recent understanding of the DC photocurrent generation in homogeneous materials without traditional p-n junctions, whose origins entangle quantum geometry and many-body electron-phonon interaction. The second consequence concerns the fate of light-induced excitons after turning off the illumination. By developing an ab initio theory for the correlated electronic system dressed by phonons, I will illustrate how excitons get trapped by themselves via excited-state dynamical relaxation, showing that the optical properties of quantum materials could be drastically changed due to these self-trapped excitons.

Bio: Dr. Zhenbang Dai is a computational physicist specialized in condensed matter physics, with a focus on developing and leveraging ab initio methods to investigate complex phenomena in materials, including charged and exciton polarons, bulk photovoltaic effect, anharmonic lattice dynamics, etc. Currently, Dr. Dai is a postdoctoral fellow in the Department of Physics and Oden Institute at The University of Texas at Austin. Prior to his current position, he earned his Ph.D. degree from the Department of Chemistry at University of Pennsylvania in 2022 and obtained his B.S. degree in materials science and engineering from Shanghai Jiao Tong University in 2017.