Probing Many-Body Interactions in Monolayer Transition-Metal Dichalcogenides

Abstract

Many-body interactions in monolayer transition-metal dichalcogenides are strongly affected by their unique band structure. We study these interactions by measuring the energy shift of neutral excitons (bound electron-hole pairs) in gated WSe${}_2$ and MoSe${}_2$. Surprisingly, while the blueshift of the neutral exciton, $X^0$, in electron-doped samples can be more than 10~meV, the blueshift in hole-doped samples is nearly absent. Taking into account dynamical screening and local-field effects, we present a transparent and analytical model that elucidates the crucial role played by intervalley plasmons in electron-doped conditions. The energy shift of $X^0$ as a function of charge density is computed showing agreement with experiment, where the renormalization of $X^0$ by intervalley plasmons yields a stronger blueshift in MoSe${}_2$ than in WSe${}_2$ due to differences in their band ordering.

Compared with the previous version, this is an entirely new paper except for the experiment part. It took us 2 more years to get the theory straight and we hope it is right this time