Collective Spin Excitations in Correlated Moir\'e Chern Ferromagnets

TL;DR

This paper explores how magnon excitations influence magnetic stability and transition temperatures in correlated moiré Chern ferromagnets, revealing topological effects that can be tuned by moiré engineering.

Contribution

It uncovers the topological nature of magnon spectra and their role in enhancing magnetic transition temperatures in moiré Chern ferromagnets.

Findings

Magnon spectrum has isolated low-energy bands with topological transitions.

Magnon gap depends on magnetic ground state topology.

Transition temperature $T_c$ is significantly higher in the quantum anomalous Hall phase.

Abstract

Moir\'e-induced narrow electronic bands in transition metal dichalcogenide superlattices support many correlated quantum phases characterized by novel charge, flavor, and topological orders. Among these, magnetic ordering emerges as the most ubiquitous, often serving as the parent state for other correlated phases, including quantum anomalous Hall states, as well as chiral superconducting state. Because of electron-electron correlation, the stability of magnetic order is critically influenced by low-energy collective spin fluctuations, or magnon excitations. We investigate the nature of magnon excitations and their impact on the stability and transition temperature of the magnetic state at integer filling factor $\nu = -1$. We find that the magnon spectrum exhibits isolated low-energy bands whose topological character undergoes a transition upon tuning the interlayer displacement field. The magnon gap is found to depend sensitively on the topology of the magnetic ground state, resulting in an order-of-magnitude enhancement of the transition temperature $T_c$ in the quantum anomalous Hall phase compared to the topologically trivial correlated insulator. Our findings provide insight into the interplay between electron and magnon topology and suggest new routes for controlling magnetism and topology via moir\'e engineering.