Spatial coherence of room-temperature monolayer WSe$_2$ exciton-polaritons in a trap

TL;DR

This paper demonstrates that monolayer WSe$_2$ in a microcavity can produce spatially and temporally coherent exciton-polaritons at room temperature, showing potential for compact coherent light sources and valleytronic devices.

Contribution

It provides experimental evidence of strong light-matter coupling and polariton lasing in monolayer WSe$_2$ at ambient conditions, with control over valley states via magnetic fields.

Findings

Observation of strong coupling regime at room temperature

Detection of polariton laser threshold behavior

Manipulation of valley-polaritons with magnetic field

Abstract

The emergence of spatial and temporal coherence of light emitted from solid-state systems is a fundamental phenomenon, rooting in a plethora of microscopic processes. It is intrinsically aligned with the control of light-matter coupling, and canonical for laser oscillation. However, it also emerges in the superradiance of multiple, phase-locked emitters, and more recently, coherence and long-range order have been investigated in bosonic condensates of thermalized light, as well as in exciton-polaritons driven to a ground state via stimulated scattering. Here, we experimentally show that the interaction between photons in a Fabry-Perot microcavity and excitons in an atomically thin WSe$_2$ layer is sufficient such that the system enters the hybridized regime of strong light-matter coupling at ambient conditions. Via Michelson interferometry, we capture clear evidence of increased spatial and temporal coherence of the emitted light from the spatially confined system ground-state. The coherence build-up is accompanied by a threshold-like behaviour of the emitted light intensity, which is a fingerprint of a polariton laser effect. Valley-physics is manifested in the presence of an external magnetic field, which allows us to manipulate K and K' polaritons via the Valley-Zeeman-effect. Our findings are of high application relevance, as they confirm the possibility to use atomically thin crystals as simple and versatile components of coherent light-sources, and in valleytronic applications at room temperature.