Electron recoil effect in electrically tunable MoSe2 monolayers

TL;DR

This study investigates the electron recoil effect in electrically tunable MoSe2 monolayers, combining experimental observations with theoretical models to understand exciton-carrier interactions and their dynamics.

Contribution

It provides the first combined experimental and theoretical analysis of the electron recoil effect in monolayer semiconductors, including time-resolved insights into non-equilibrium states.

Findings

Cooling of overheated populations occurs on picosecond timescales

Lattice temperature and free carrier density influence relaxation dynamics

Correlation between recoil relaxation times and luminescence rise times

Abstract

Radiative recombination of excitons dressed by the interactions with free charge carriers often occurs under simultaneous excitation of either electrons or holes to unbound states. This phenomenon, known as the electron recoil effect, manifests itself in pronounced, asymmetric spectral lineshapes of the resulting emission. We study the electron recoil effect experimentally in electrically-tunable monolayer semiconductors and derive it theoretically using both trion and Fermi-polaron pictures. Time-resolved analysis of the recoil lineshapes is employed to access transient, non-equilibrium states of the exciton-carrier complexes. We demonstrate cooling of the initially overheated populations on the picosecond timescales and reveal the impact of lattice temperature and free carrier density. Both thermally activated phonons and the presence of free charges are shown to accelerate equilibration. Finally, we find strong correlations between relaxation times from recoil analysis and luminescence rise times, providing a consistent interpretation for the initial dynamics of trion/Fermi-polaron states.