Exciton-phonon coupling in MoSe2 monolayers

TL;DR

This paper investigates the exciton-phonon interactions in MoSe2 monolayers, combining experimental measurements and analytical theory to understand their impact on optical properties and estimate deformation potentials.

Contribution

It provides a new analytical model for exciton-phonon coupling in MoSe2 and demonstrates its effectiveness in fitting spectra and understanding coupling strength.

Findings

High-resolution spectra reveal extended high-energy tails due to exciton-phonon interactions.

Theoretical model successfully fits absorption and emission spectra, estimating deformation potentials.

Enhanced exciton-phonon coupling in 2D TMDs compared to quantum wells.

Abstract

We study experimentally and theoretically the exciton-phonon interaction in MoSe2 monolayers encapsulated in hexagonal BN, which has an important impact on both optical absorption and emission processes. The exciton transition linewidth down to 1 meV at low temperatures makes it possible to observe high energy tails in absorption and emission extending over several meV, not masked by inhomogeneous broadening. We develop an analytical theory of the exciton-phonon interaction accounting for the deformation potential induced by the longitudinal acoustic phonons, which plays an important role in exciton formation. The theory allows fitting absorption and emission spectra and permits estimating the deformation potential in MoSe2 monolayers. We underline the reasons why exciton-phonon coupling is much stronger in two-dimensional transition metal dichalcodenides as compared to conventional quantum well structures. The importance of exciton-phonon interactions is further highlighted by the observation of a multitude of Raman features in the photoluminescence excitation experiments.