Magnetic Control of Valley Pseudospin in Monolayer WSe2

TL;DR

This paper demonstrates magnetic control over valley pseudospin in monolayer WSe2 through magneto-photoluminescence, revealing valley Zeeman splitting, magnetic tuning of polarization, and insights into magnetic moments and excitonic interactions.

Contribution

It provides the first experimental evidence of magnetic manipulation of valley pseudospin in monolayer WSe2, including detailed analysis of magnetic moments and excitonic effects.

Findings

Observation of valley Zeeman splitting in WSe2

Magnetic tuning of valley polarization and coherence

Differences in magnetic response between neutral and charged excitons

Abstract

Local energy extrema of the bands in momentum space, or valleys, can endow electrons in solids with pseudo-spin in addition to real spin. In transition metal dichalcogenides this valley pseudo-spin, like real spin, is associated with a magnetic moment which underlies the valley-dependent circular dichroism that allows optical generation of valley polarization, intervalley quantum coherence, and the valley Hall effect. However, magnetic manipulation of valley pseudospin via this magnetic moment, analogous to what is possible with real spin, has not been shown before. Here we report observation of the valley Zeeman splitting and magnetic tuning of polarization and coherence of the excitonic valley pseudospin, by performing polarization-resolved magneto-photoluminescence on monolayer WSe2. Our measurements reveal both the atomic orbital and lattice contributions to the valley orbital magnetic moment; demonstrate the deviation of the band edges in the valleys from an exact massive Dirac fermion model; and reveal a striking difference between the magnetic responses of neutral and charged valley excitons which is explained by renormalization of the excitonic spectrum due to strong exchange interactions.