Pseudospin-valley coupled edge states in a photonic topological insulator

TL;DR

This paper demonstrates a ballistic edge state in a photonic topological insulator where pseudospin and valley degrees of freedom are locked to propagation direction, enabling robust optical signal transport and control.

Contribution

It reports the experimental observation of spin-valley locked edge states and suppression of inter-valley scattering in photonic topological insulators, advancing optical encoding techniques.

Findings

Observation of spin-valley locked edge states

Inhibition of inter-valley scattering at Y-junctions

Potential for valley-based optical signal control

Abstract

Pseudo-spin and valley degrees of freedom (DOFs) engineered in photonic analogues of topological insulators (TI) provide potential approaches to optical encoding and robust signal transport. Here we observe a ballistic edge state whose spin-valley indices are locked to the direction of propagation along the interface between a valley photonic crystal and a metacrystal emulating the quantum spin Hall effect. We demonstrate the inhibition of inter-valley scattering at a Y-junction formed at the interfaces between photonic TIs carrying different spin-valley Chern numbers. These results open up the possibility of using the valley DOF to control the flow of optical signals in 2D structures.