Observation of bosonic condensation in a hybrid monolayer MoSe<sub>2</sub>-GaAs microcavity.

Waldherr, Max; Lundt, Nils; Klaas, Martin; Betzold, Simon; Wurdack, Matthias; Baumann, Vasilij; Estrecho, Eliezer; Nalitov, Anton et al. · Nat Commun · 2018

basic_science · Level V

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Abstract

Bosonic condensation belongs to the most intriguing phenomena in physics, and was mostly reserved for experiments with ultra-cold quantum gases. More recently, it became accessible in exciton-based solid-state systems at elevated temperatures. Here, we demonstrate bosonic condensation driven by excitons hosted in an atomically thin layer of MoSe<sub>2</sub>, strongly coupled to light in a solid-state resonator. The structure is operated in the regime of collective strong coupling between a Tamm-plasmon resonance, GaAs quantum well excitons, and two-dimensional excitons confined in the monolayer crystal. Polariton condensation in a monolayer crystal manifests by a superlinear increase of emission intensity from the hybrid polariton mode, its density-dependent blueshift, and a dramatic collapse of the emission linewidth, a hallmark of temporal coherence. Importantly, we observe a significant spin-polarization in the injected polariton condensate, a fingerprint for spin-valley locking in monolayer excitons. Our results pave the way towards highly nonlinear, coherent valleytronic devices and light sources.