Unraveling the excitonic states in bulk 2H−MoS2 via their giant Stark shift

Abstract

The interlayer exciton ($IL$) in bilayer $2H\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ has earlier been shown to undergo large Stark splitting under electric field ${F}_{z}\ensuremath{\parallel}\mathbf{c}$ axis. We show that the excited state exciton ${A}_{2s}$ in bulk $2H\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$ undergoes nearly three times as large splitting, with a dipole moment magnitude 1.46 enm. The nature and evolution of different exciton species with ${F}_{z}$ is verified by comparison with ab initio GW-Bethe-Salpheter equation (BSE) calculations that include the full electron-hole correlations. The excitonic wave functions reveal the individual character of the exciton states at high ${F}_{z}$ as the ground state ${A}_{1s}$, split interlayer $I{L}_{\ensuremath{-}}, I{L}_{+}$, and split excited state ${A}_{2s\ensuremath{-}}$. Extrapolation to low ${F}_{z}$ indicates that $IL$ and ${A}_{2s}$ mix strongly. We try to rationalize the large dipole moment values by comparing GW-BSE results with the hydrogenic exciton model. Although the dominant ${A}_{1s}$ shows an insignificant Stark shift, its large anticrossing with ${A}_{2s\ensuremath{-}}$ provides a pathway for its modulation and control using an electric field.