Fast Relaxation of Photo-Excited Carriers in 2-D Transition Metal Dichalcogenides

We predict a fast relaxation of photo-excited carriers in monolayer transition metal dichalcogenides, which is mediated by the emission of longitudinal optical (LO) and homopolar (HP) phonons. By evaluating Born effective charges for MoS
₂
, MoSe
₂
, WS
₂
, and WSe
₂
, we find that, due to the polar coupling of electrons with LO phonons, and the HP phonons lattice deformation potential, the cooling times for hot electrons and holes from excitation energies of several hundred meV are at ps-scale.