Quantum spin Hall effect in bilayer honeycomb lattices with C-type antiferromagnetic order

TL;DR

This paper proposes a new bilayer honeycomb lattice system exhibiting quantum spin Hall effects that are protected by PT symmetry, despite broken time-reversal symmetry, with potential for tunable topological phases and observable edge states.

Contribution

It introduces a novel scheme combining spin-orbit coupling and magnetic order to realize PT-symmetry-protected quantum spin Hall insulators in bilayer honeycomb lattices.

Findings

Identification of a topological phase diagram for the system

Observation of quantized resistance indicating helical edge states

Protection of the phase by interlayer PT symmetry despite broken T symmetry

Abstract

We propose a scheme to realize time-reversal symmetry-broken quantum spin Hall insulators using bilayer honeycomb lattices, combining intrinsic spin-orbit coupling, C-type antiferromagnetic ordering, and staggered potentials. The C-type antiferromagnetic order emerges from the interplay between intralayer antiferromagnetism and interlayer ferromagnetism. The system's topological properties are characterized by the spin Chern number. We present the topological phase diagram of the bilayer honeycomb lattice, providing a detailed insight into the stability and tunability of the quantum spin Hall effect in this system. The presence of helical edge states is confirmed by the measurement of quantized longitudinal resistance values of 3/2(h/e2) and 1/2(h/e2) in a sixterminal Hall-bar device. Remarkably, this quantum spin Hall insulator phase is protected by interlayer parity-time (PT) symmetry, despite the breaking of time-reversal symmetry.