Picosecond Electronic and Structural Dynamics in Photoexcited Monolayer MoSe₂

Monolayers of semiconducting transition metal dichalcogenides (TMDC) are emerging as strong candidate materials for next generation electronic and optoelectronic devices. Prior studies have demonstrated strong light-matter interactions in these materials which suggests optical control of material properties is a promising route for their functionalization. However, the electronic and structural dynamics in response to electronic excitation have not yet been fully elucidated. In this work, we use non-adiabatic quantum molecular dynamics based on time-dependent density functional theory to study lattice dynamics of a model TMDC monolayer of MoSe₂ after electronic excitation and explore the dependence of dynamics on photo-generated electron-hole density. We observe phonon mode softening induced by Fermi-surface nesting, as well as increasing lattice disorder, as measured by the Debye-Waller factor (DWF), with increasing excitation. Furthermore, we find a transition from single-exponential to bi-exponential decay of the DWF at higher electron-hole densities.