Insights on magnon topology and valley-polarization in 2D bilayer quantum magnets

TL;DR

This paper explores the topological properties and valley-polarization of magnons in 2D bilayer quantum magnets, revealing how stacking, symmetry, and spin-orbit coupling influence their topological phases and transport phenomena.

Contribution

It provides a comprehensive analysis of magnon topology in honeycomb bilayers, highlighting the effects of SOC, stacking, and symmetry breaking on topological phases and transport properties.

Findings

Identification of stacking-dependent topological phases

Prediction of unconventional Hall and Nernst effects

Discovery of bandgap closures with topological implications

Abstract

The rich and unconventional physics in layered 2D magnets can open new avenues for topological magnonics and magnon valleytronics. In particular, two-dimensional (2D) bilayer quantum magnets are gaining increasing attention due to their intriguing stacking-dependent magnetism, controllable ground states, and topological excitations induced by magnetic spin-orbit couplings (SOCs). Despite the substantial research on these materials, their topological features remain widely unexplored to date. The present study comprehensively investigates the magnon topology and magnon valley-polarization in honeycomb bilayers with collinear magnetic order. We elucidate the separate and combined effects of the SOC, magnetic ground-states, stacking order, and inversion symmetry breaking on the topological phases, magnon valley transport, and the Hall and Nernst effects. The comprehensive analysis suggests clues to determine the SOC's nature and predicts unconventional Hall and Nernst conductivities in topologically trivial phases. We further report on novel bandgap closures in layered antiferromagnets and detail their topological implications. We believe the present study provides important insights into the fundamental physics and technological potentials of topological 2D magnons.