Strain control of exciton and trion spin-valley dynamics in monolayer transition metal dichalcogenides

Zhao An, Pedro Soubelet, Yaroslav Zhumagulov, Michael Zopf, Alex Delhomme, Chenjiang Qian, Paulo E. Faria Junior, Jaroslav Fabian, Xin Cao, Jingzhong Yang, Andreas V. Stier, Fei Ding, Jonathan J. Finley

Published 2023-03-27Version 1

The electron-hole exchange interaction is a fundamental mechanism that drives valley depolarization via intervalley exciton hopping in semiconductor multi-valley systems. Here, we report polarization-resolved photoluminescence spectroscopy of neutral excitons and negatively charged trions in monolayer MoSe$_2$ and WSe$_2$ under biaxial strain. We observe a marked enhancement(reduction) on the WSe$_2$ triplet trion valley polarization with compressive(tensile) strain while the trion in MoSe$_2$ is unaffected. The origin of this effect is shown to be a strain dependent tuning of the electron-hole exchange interaction. A combined analysis of the strain dependent polarization degree using ab initio calculations and rate equations shows that strain affects intervalley scattering beyond what is expected from strain dependent bandgap modulations. The results evidence how strain can be used to tune valley physics in energetically degenerate multi-valley systems.