Ultrafast photo-induced lattice dynamics in MoTe_2 studied using ab-initio MD simulations and MeV Ultrafast Electron Diffraction (MUED)*

Transition metal dichalcogenides (TMDs) like MoTe_2 show promising high electron mobilities and light-induced phase transitions involving their metastable trigonal 1T’ and Td phases could be used for photo-induced fast switching in electronic devices. Absorbed laser energy alters electronic properties and initiates ultrafast lattice dynamics, but the detailed mechanisms of the dynamics and under what conditions they lead to phase transitions remains unclear. Here, we performed ab-initio MD simulations of laser-excited MoTe_2 in the 1T' and T_d phases (which differ by stacking) and some mixed phases involving stacking faults. We compute the time evolution of Bragg peak intensities to identify contributions of each phase after the excitation and determine intensity thresholds for which nonthermal phase transitions are initiated. Moreover, by comparing computed Bragg peak intensities to time-dependent Bragg peak intensities measured via MUED experiments, we identify contributions in the experiment from thermal and nonthermal lattice dynamics, stacking faults, and possible phase transitions. Understanding these processes gives insight into the ultrafast control of structural and electronic properties in metastable 2D TMDs.