Breaking of valley degeneracy by magnetic field in monolayer MoSe2

TL;DR

This study demonstrates how an out-of-plane magnetic field breaks valley degeneracy in monolayer MoSe2, enabling control over valley polarization through optical and electrical means, with potential applications in valleytronics.

Contribution

It provides experimental evidence of magnetic field-induced valley degeneracy breaking and shows control of valley polarization via magnetic field and gate voltage in monolayer MoSe2.

Findings

Linear valley splitting of -0.22 meV/T observed

Magnetic field controls luminescence handedness

Valley degeneracy breaking demonstrated in monolayer MoSe2

Abstract

Using polarization-resolved photoluminescence spectroscopy, we investigate valley degeneracy breaking by out-of-plane magnetic field in back-gated monolayer MoSe$_2$ devices. We observe a linear splitting of $-0.22 \frac{\text{meV}}{\text{T}}$ between luminescence peak energies in $\sigma_{+}$ and $\sigma_{-}$ emission for both neutral and charged excitons. The optical selection rules of monolayer MoSe$_2$ couple 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 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.