Cubic 3D Chern photonic insulators with orientable large Chern vectors

Chiara Devescovi,Mikel García-Díez,Barry Bradlyn,Maia G. Vergniory,Jon Lasa-Alonso,Iñigo Robredo,Aitzol García-Etxarri,María Blanco de Paz,Juan L. Mañes

doi:10.1038/s41467-021-27168-w

Abstract

Time Reversal Symmetry (TRS) broken topological phases provide gapless surface states protected by topology, regardless of additional internal symmetries, spin or valley degrees of freedom. Despite the numerous demonstrations of 2D topological phases, few examples of 3D topological systems with TRS breaking exist. In this article, we devise a general strategy to design 3D Chern insulating (3D CI) cubic photonic crystals in a weakly TRS broken environment with orientable and arbitrarily large Chern vectors. The designs display topologically protected chiral and unidirectional surface states with disjoint equifrequency loops. The resulting crystals present the following characteristics: First, by increasing the Chern number, multiple surface states channels can be supported. Second, the Chern vector can be oriented along any direction simply changing the magnetization axis, opening up larger 3D CI/3D CI interfacing possibilities as compared to 2D. Third, by lowering the TRS breaking requirements, the system is ideal for realistic photonic applications where the magnetic response is weak.

Highlights

Time Reversal Symmetry (TRS) broken topological phases provide gapless surface states protected by topology, regardless of additional internal symmetries, spin or valley degrees of freedom
In contrast to 2D, a 3D Chern insulator (3D Chern insulators (CI)) is a topological phase that can be characterized by three first Chern invariants–or a Chern vector C = (Cx, Cy, Cz) - defined on lower dimensional surfaces[24,25,26]: such a state of matter can support chiral surface states propagating on the planes with Miller indices indicated by the Chern vector
The starting point of our design is a photonic crystal with a unit cell containing four dielectric rods directed along the main diagonals of a cubic crystal

Summary

Introduction

Time Reversal Symmetry (TRS) broken topological phases provide gapless surface states protected by topology, regardless of additional internal symmetries, spin or valley degrees of freedom. Among all topological states of matter, timereversal symmetry (TRS) broken topological materials, such as Chern insulators (CI)[2,3] and lasers[14], have been a particular focus due to their topologically protected unidirectional edge states with non-reciprocal propagation properties In these systems, scattering processes from one boundary state into another are strongly suppressed, due to decoupling of counter-propagating 1D chiral edge channels[15,16]. The Chern vector was fixed to have a single component along a preferred axis selected by the fabrication, a situation similar to that of a stack of 2D Chern layers This design required strong TRS breaking, which is usually an arduous challenge in photonic crystals.

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Results