# Chiral light-matter interactions using spin-valley states in transition metal dichalcogenides

## TL;DR

This paper demonstrates chiral light-matter interactions in a dielectric waveguide using spin-valley states in transition metal dichalcogenides, enabling directional light emission without external magnetic fields.

## Contribution

It introduces a novel system coupling monolayer WSe2 to a chiral photonic crystal waveguide, achieving high directionality in emission based on valley-dependent polarization.

## Key findings

- Achieved directional emission with a directionality of 0.35.
- Coupled monolayer WSe2 to a chiral dielectric waveguide.
- Enabled on-chip control of light directionality.

## Abstract

Chiral light-matter interactions can enable polarization to control the direction of light emission in a photonic device. Most realizations of chiral light-matter interactions require external magnetic fields to break time-reversal symmetry of the emitter. One way to eliminate this requirement is to utilize strong spin-orbit coupling present in transition metal dichalcogenides that exhibit a valley dependent polarized emission. Such interactions were previously reported using plasmonic waveguides, but these structures exhibit short propagation lengths due to loss. Chiral dielectric structures exhibit much lower loss levels and could therefore solve this problem. We demonstrate chiral light-matter interactions using spin-valley states of transition metal dichalcogenide monolayers coupled to a dielectric waveguide. We use a photonic crystal glide plane waveguide that exhibits chiral modes with high field intensity, coupled to monolayer WSe2. We show that the circularly polarized emission of the monolayer preferentially couples to one direction of the waveguide, with a directionality as high as 0.35, limited by the polarization purity of the bare monolayer emission. This system enables on-chip directional control of light and could provide new ways to control spin and valley degrees of freedom in a scalable photonic platform.

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Source: https://tomesphere.com/paper/1904.12349