Ultrafast, Excitation-induced Effects in Semiconductor Nanostructures

Excitation-induced many-body effects play an important role in semiconductor quantum materials, where ultrafast processes determine the system properties. These effects occur when light excitations dynamically alter light absorption and emission, leading to nonlinear, excitation-induced changes in a semiconductor’s optical response. This work theoretically investigates ultrafast excitation-induced effects in semiconductor nanostructures. Specifically, using a first-principles analysis based on quantum dynamic cluster expansion, we implement  a systematic approach to describe the dynamics of microscopic polarizations and carrier occupations in semiconductor quantum materials precisely. We explore the dynamic buildup of excitation induced effects, and propose a method to measure their build-up time via ultrafast experiments. Utilizing these theoretical tools, we successfully guided experiments to detect ultrafast processes. This included observing the time-delayed buildup of dephasing that facilitated ultrafast switching and identifying nonperturbative ultrafast nonlinearities, which are crucial for quantum photonic applications. Our findings offer significant insights into the fundamental quantum processes relevant to ultrafast photonics and open up new possibilities for quantum information and quantum optoelectronics technologies.

CHAIR: Professor Mackillo Kira