Chiral Valley Edge States

TL;DR

This paper introduces chiral valley edge states in photonic systems, enabling backscattering-free, valley-polarized wave propagation and multiplexing, thus advancing robust valley-based information processing.

Contribution

It proposes and experimentally demonstrates chiral valley edge states that combine topological protection with valley DoF control, enabling valley multiplexing in photonic crystals.

Findings

Successful experimental realization in photonic crystals

Demonstration of valley (de-)multiplexer and waveguide crossing

Achieved backscattering-free, valley-polarized wave propagation

Abstract

Valleytronics has emerged as a promising paradigm, enabling comprehensive control of the valley degree of freedom (DoF) for energy-efficient and high-speed information processing. However, backscattering-induced valley depolarization remains a fundamental limitation, stemming from the weak topological protection of the valley Hall phase. Here, we propose and demonstrate the concept of chiral valley edge states, which integrate the robust unidirectional chiral edge states with valley DoF. By controlling the valley Dirac masses, we selectively confine the chiral edge band around a single valley, enabling back-scattering-free propagation while imparting valley polarization. Our strategy not only addresses the valley depolarization issue but also introduces a unique functionality--valley multiplexing--allowing independent and arbitrary control over waves associated with different valley polarizations. We demonstrate our concept experimentally within hybrid topological photonic crystal systems composed of Chern and valley photonic crystals. Moreover, two key components for valley multiplexing are demonstrated: a valley (de-)multiplexer and a valley-locked waveguide crossing, facilitating non-interfering signal routing. Our results establish a novel interplay between the topological quantum Hall and valley Hall phases, offering a new framework for robust valley-based information processing.