Simulation of ultrafast spin and valley dynamics in two-dimensional materials

We present simulations of how optical experiments probe the spin and valley dynamics in two-dimensional materials - such as single-layer transition metal dichalcogenides (MoS₂, WS₂ and WSe₂). For the simulations, we have developed an ab initio implementation of time-dependent many-body perturbation theory. Simulations include the photo-generation of electrons and holes and the subsequent carrier dynamics, including the scattering mechanisms induced by electron-phonon and electron-electron interactions. We show simulations of pump-probe ultrafast spectroscopy experiments such as time-dependent Kerr rotation [1] and two-colour helicity-resolved pump-probe spectroscopy [2]. We can simulate the selective optical excitation of electron and holes in different valleys of the Brillouin zone. Our simulations shed light on the understanding of the mechanisms driving the intravalley and intervalley spin relaxation dynamics and the valley polarization dynamics in single-layer transition metal dichalcogenides. We demonstrate that the dynamics is largely driven by electron-phonon coupling and obtain good quantitative agreement with the experiments.