Twisted quadrupole topological photonic crystals

TL;DR

This paper introduces a novel method to realize quadrupole topological photonic crystals through twisting degrees-of-freedom, enabling higher-order topological wave trapping without flux-threading, and broadening topological photonics applications.

Contribution

It demonstrates that twisting a trivial photonic crystal induces quadrupole topological phases, expanding the design principles for topological photonic devices.

Findings

Twisting induces quadrupole topological phases in photonic crystals.

Versatile edge and corner states are controllable via twisting angles.

The approach enables topological phenomena without flux-threading.

Abstract

Topological manipulation of waves is at the heart of the cutting-edge metamaterial researches. Quadrupole topological insulators were recently discovered in two-dimensional (2D) flux-threading lattices which exhibit higher-order topological wave trapping at both the edges and corners. Photonic crystals (PhCs), lying at the boundary between continuous media and discrete lattices, however, are incompatible with the present quadrupole topological theory. Here, we unveil quadrupole topological PhCs triggered by a twisting degree-of-freedom. Using a topologically trivial PhC as the motherboard, we show that twisting induces quadrupole topological PhCs without flux-threading. The twisting-induced crystalline symmetry enriches the Wannier polarizations and lead to the anomalous quadrupole topology. Versatile edge and corner phenomena are observed by controlling the twisting angles in a lateral heterostructure of 2D PhCs. Our study paves the way toward topological twist-photonics as well as the quadrupole topology in the quasi-continuum regime for phonons and polaritons.