Encapsulation Narrows Excitonic Homogeneous Linewidth of Exfoliated MoSe$_2$ Monolayer

TL;DR

Encapsulation of MoSe₂ monolayers in hexagonal boron nitride significantly narrows the excitonic homogeneous linewidth by reducing inhomogeneity and non-radiative processes, enhancing optical coherence and stability.

Contribution

This study provides the first direct measurement of homogeneous linewidth in encapsulated MoSe₂ monolayers, demonstrating the effects of encapsulation on excitonic coherence and sample stability.

Findings

Encapsulation reduces homogeneous linewidth to 0.26 meV.

Encapsulation suppresses non-radiative processes and inhomogeneity.

Encapsulated samples are more resilient to temperature cycling and optical excitation.

Abstract

The excitonic homogeneous linewidth of an exfoliated monolayer MoSe$_2$ encapsulated in hexagonal boron nitride is directly measured using multidimensional coherent spectroscopy with micron spatial resolution. The linewidth is 0.26 $\pm$ 0.02 meV, corresponding to a dephasing time $T_2 \approx$ 2.5 ps, which is almost half the narrowest reported values for non-encapsulated MoSe$_2$ flakes. We attribute the narrowed linewidth to Coulomb screening by the encapsulated material and suppression of non-radiative processes. Through direct measurements of encapsulated and non-encapsulated monolayers, we confirm that encapsulation reduces the sample inhomogeneity. However, linewidths measured using photoluminescence and linear absorption remain dominated by inhomogeneity, and these linewidths are roughly 5 times larger than the homogeneous linewidth in even the highest-quality encapsulated materials. The homogeneous linewidth of non-encapsulated monolayers is very sensitive to temperature cycling, whereas encapsulated samples are not modified by temperature cycling. The nonlinear signal intensity of non-encapsulated monolayers is degraded by high-power optical excitation, whereas encapsulated samples are very resilient to optical excitation with optical powers up to the point of completely bleaching the exciton.