Spin-dependent gain and loss in photonic quantum spin Hall systems

TL;DR

This paper explores how non-Hermitian effects in a photonic quantum spin Hall system influence gain, loss, and the behavior of topological edge and corner modes, revealing new dynamical properties related to spin.

Contribution

It introduces non-reciprocal intracell couplings in a honeycomb lattice to control gain, loss, and mode localization, advancing understanding of non-Hermitian topological phases with spin.

Findings

Non-reciprocal couplings induce gain in one pseudo-spin and loss in the other.

Such couplings suppress spin mixing and delocalize corner modes.

The work enhances understanding of non-Hermitian topological dynamics with spin.

Abstract

Topological phases are greatly enriched by including non-Hermiticity. While most works focus on the topology of the eigenvalues and eigenstates, how topologically nontrivial non-Hermitian systems behave in dynamics has only drawn limited attention. Here, we consider a breathing honeycomb lattice known to emulate the quantum spin Hall effect and exhibits higher-order corner modes. We find that non-reciprocal intracell couplings introduce gain in one pseudo-spin subspace while loss with the same magnitude in the other. In addition, non-reciprocal intracell couplings can also suppress the spin mixture of the edge modes at the boundaries and delocalize the higher-order corner mode. Our findings deepen the understanding of non-Hermitian topological phases and bring in the spin degree of freedom in manipulating the dynamics in non-Hermitian systems.