Photonic chiral bulk transports manipulated by boundary freedom in three-dimensional meta-crystals

TL;DR

This paper demonstrates that boundary conditions in three-dimensional photonic meta-crystals can be used to control chiral bulk transport phenomena, revealing a new degree of freedom in topological photonics.

Contribution

It introduces the concept that boundary freedom can manipulate topological bulk transports in 3D meta-crystals, supported by analytical and experimental validation.

Findings

Boundary conditions influence chiral bulk transport in photonic crystals.

Experimental validation confirms opposite chiral transports under different boundaries.

Mirror symmetry is preserved despite boundary-induced transport changes.

Abstract

In topological physics, one of the most intriguing phenomena is the presence of topological boundary states, accurately predicted by the well-established bulk-edge correspondence. For example, in three-dimensional Weyl semimetals, Fermi arcs emerge to connect projected Weyl points on the surface due to inheriting the bulk-edge correspondence from the integer quantum Hall effect. However, limited attention has been paid to exploring the reverse mechanism in topological crystals. In this study, we propose that boundaries can serve as an alternative degree of freedom to manipulate topological bulk transports. We analytically and experimentally validate our concept using a finite-thickness photonic meta-crystal that supports bulk nodal lines, with its zeroth modes exhibiting opposite chiral bulk transports under different boundary conditions. Notably, the mirror symmetry remains preserved across both configurations. These findings are applicable to other topological systems, providing new insights into systems with varied boundary conditions and offering the potential for the design of more compact and spatially efficient topological photonic devices.