# Spin-momentum locked modes on anti-phase boundaries in photonic crystals

## TL;DR

This paper demonstrates spin-momentum locking in photonic crystal edge modes on anti-phase boundaries, showing unidirectional propagation, band inversion effects, and optimized excitation methods for high directivity.

## Contribution

It introduces the concept of spin-momentum locked modes on anti-phase boundaries in photonic crystals and explores their properties and control mechanisms.

## Key findings

- Unidirectional edge mode propagation due to spin-momentum locking
- Band inversion causes propagation direction change
- Optimized source achieves high directivity in excitation

## Abstract

An anti-phase boundary is formed by shifting a portion of photonic crystal lattice along the direction of periodicity. A spinning magnetic dipole is applied to excite edge modes on the anti-phase boundary. We show the unidirectional propagation of the edge modes which is also known as spin-momentum locking. Band inversion of the edge modes is discovered when we sweep the geometrical parameters, which leads to a change in the propagation direction. Also, an optimized source is applied to excite the unidirectional edge mode with high directivity.