# Optical valley Hall effect for highly valley-coherent exciton-polaritons in an atomically thin semiconductor

## TL;DR

This paper demonstrates a macroscopic optical valley Hall effect in atomically thin MoSe2 coupled to a microcavity, enabling valley-selective exciton-polariton propagation without external magnetic fields.

## Contribution

It introduces the first observation of a macroscopic optical valley Hall effect in a strongly coupled atomically thin semiconductor system.

## Key findings

- Valley-selective expansion of exciton-polaritons observed
- The effect occurs without external magnetic fields
- Potential for spin-valley locked photonic devices

## Abstract

Spin-orbit coupling is a fundamental mechanism that connects the spin of a charge carrier with its momentum. Likewise, in the optical domain, a synthetic spin-orbit coupling is accessible, for instance, by engineering optical anisotropies in photonic materials. Both, akin, yield the possibility to create devices directly harnessing spin- and polarization as information carriers. Atomically thin layers of transition metal dichalcogenides provide a new material platform which promises intrinsic spin-valley Hall features both for free carriers, two-particle excitations (excitons), as well as for photons. In such materials, the spin of an exciton is closely linked to the high-symmetry point in reciprocal space it emerges from. Here, we demonstrate, that spin, and hence valley selective propagation is accessible in an atomically thin layer of MoSe2, which is strongly coupled to a microcavity photon mode. We engineer a wire-like device, where we can clearly trace the flow, and the helicity of exciton-polaritons expanding along a channel. By exciting a coherent superposition of K and K- tagged polaritons, we observe valley selective expansion of the polariton cloud without neither any applied external magnetic fields nor coherent Rayleigh scattering. Unlike the valley Hall effect for TMDC excitons, the observed optical valley Hall effect (OVHE) strikingly occurs on a macroscopic scale, and clearly reveals the potential for applications in spin-valley locked photonic devices.

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Source: https://tomesphere.com/paper/1902.07620