Radiative and Non-Radiative Exciton Energy Transfer in Monolayers of Two-Dimensional Transition Metal Dichalcogenides

TL;DR

This study investigates both radiative and non-radiative exciton energy transfer mechanisms in monolayer TMDs, revealing ultrafast transfer rates influenced by exciton properties and interlayer distance, with implications for energy exchange in 2D materials.

Contribution

The paper provides a unified Green's function framework to analyze exciton energy transfer in TMD monolayers, accounting for both radiative and non-radiative processes and exciton dispersion modifications.

Findings

Energy transfer times can be less than 100 femtoseconds to tens of picoseconds.

Transfer rates are comparable inside the light cone but differ outside, favoring longitudinal excitons.

Room temperature transfer times can be under a picosecond for small interlayer separations.

Abstract

We present results on the rates of interlayer energy transfer between excitons in two-dimensional transition metal dichalcogenides (TMDs). We consider both radiative (mediated by real photons) and non-radiative (mediated by virtual photons) mechanisms of energy transfer using a unified Green's function approach that takes into account modification of the exciton energy dispersions as a result of interactions. The large optical oscillator strengths associated with excitons in TMDs result in very fast energy transfer rates. The energy transfer times depend on the exciton momentum, exciton linewidth, and the interlayer separation and can range from values less than 100 femtoseconds to more than tens of picoseconds. Whereas inside the light cone the energy transfer rates of longitudinal and transverse excitons are comparable, outside the light cone the energy transfer rates of longitudinal excitons far exceed those of transverse excitons. Average energy transfer times for a thermal ensemble of longitudinal and transverse excitons is temperature dependent and can be smaller than a picosecond at room temperature for interlayer separations smaller than 10 nm. Energy transfer times of localized excitons range from values less than a picosecond to several tens of picoseconds. When the exciton scattering and dephasing rates are small, energy transfer dynamics exhibit coherent oscillations. Our results show that electromagnetic interlayer energy transfer can be an efficient mechanism for energy exchange between TMD monolayers.