Breaking of Valley Degeneracy by Magnetic Field in MonolayerMoSe2

Abstract

Using polarization-resolved photoluminescence spectroscopy, we investigate the breaking of valley degeneracy by an out-of-plane magnetic field in back-gated monolayer ${\mathrm{MoSe}}_2$ devices. We observe a linear splitting of $-0.22\mathrm{meV}/\mathrm{T}$ between luminescence peak energies in ${\sigma }_{+}$ and ${\sigma }_{-}$ emission for both neutral and charged excitons. The optical selection rules of monolayer ${\mathrm{MoSe}}_2$ couple the photon handedness to the exciton valley degree of freedom; so this splitting demonstrates valley degeneracy breaking. In addition, we find that the luminescence handedness can be controlled with a magnetic field to a degree that depends on the back-gate voltage. An applied magnetic field, therefore, provides effective strategies for control over the valley degree of freedom.