Moir\'e magnons in twisted bilayer magnets with collinear order

TL;DR

This paper investigates moiré magnon bands in twisted bilayer magnets with collinear order, revealing flat topological bands and potential for novel thermal spin transport phenomena.

Contribution

It introduces the study of moiré magnon bands in twisted bilayer magnets with Dzyaloshinskii-Moriya interactions, highlighting their topological properties and thermal transport implications.

Findings

Valley moiré bands are extremely flat across various twist angles.

Topological Chern numbers of flat bands vary with twist angle.

Topological flat bands enable nontrivial thermal spin transport.

Abstract

We explore the moir\'e magnon bands in twisted bilayer magnets with next-nearest neighboring Dzyaloshinskii-Moriya interactions, assuming that the out-of-plane collinear magnetic order is preserved under weak interlayer coupling. By calculating the magnonic band structures and the topological Chern numbers for four representative cases, we find that (i) the valley moir\'e bands are extremely flat over a wide range of continuous twist angles; (ii) the topological Chern numbers of the lowest few flat bands vary significantly with the twist angle; and (iii) the lowest few topological flat bands in bilayer antiferromagnets entail nontrivial thermal spin transport in the transverse direction; These properties make twisted bilayer magnets an ideal platform to study the magnonic counterparts of moir\'e electrons, where the statistical distinction between magnons and electrons leads to fundamentally new physical behavior.