Superior valley polarization and coherence of 2s excitons in monolayer WSe2

TL;DR

This study demonstrates robust 2s exciton emission in monolayer WSe2 with superior valley polarization and coherence, revealing insights into valley depolarization mechanisms relevant for quantum valleytronics.

Contribution

First experimental observation of 2s exciton emission in monolayer WSe2 showing enhanced valley properties and insights into Coulomb-exchange-driven depolarization.

Findings

2s excitons persist up to 150K

2s excitons exhibit higher valley polarization than 1s

Evidence for Coulomb-exchange-driven valley depolarization mechanism

Abstract

We report experimental observation of 2s exciton radiative emission from monolayer tungsten diselenide, enabled by hexagonal boron nitride protected high-quality samples. The 2s luminescence is highly robust and persists up to 150K, offering a new quantum entity for manipulating the valley degree of freedom. Remarkably, the 2s exciton displays superior valley polarization and coherence than 1s under similar experimental conditions. This observation provides evidence that the Coulomb-exchange-interaction-driven valley-depolarization process, the Maialle-Silva-Sham mechanism, plays an important role in valley excitons of monolayer transition metal dichalcogenides.