Enhanced Interlayer Exciton Lifetime and Temporal Coherence in Free-Standing WSe2/WS2 Heterobilayers

Abstract

Transition metal dichalcogenide heterobilayers are highly susceptible to external perturbations, leading to pronounced variations in their optical properties. While recent studies have shown that suspending heterobilayers in air significantly enhances the formation efficiency of interlayer excitons (IXs), the systematic investigation of the substrate effect on other fundamental optical properties, such as photoluminescence (PL) line width, spontaneous emission lifetime, and exciton dephasing time at cryogenic temperatures, remains unexplored. Here, we investigate the optical properties of IXs in a substrate-free environment by fabricating heterobilayers on a hole-patterned substrate. Owing to reduced dielectric screening and the suppression of substrate-induced nonradiative decay channels, we observed strongly enhanced IX PL emission, a 2-fold narrowing of the line width, and prolonged emission lifetimes in suspended regions. Furthermore, we report for the first time measurements of IX dephasing times in free-standing heterobilayers, revealing a 2-fold enhancement arising from the removal of deformation-potential coupling between excitons and substrate phonons. Overall, our results highlight the crucial role of the substrate in governing the emission dynamics of IXs.