Itinerant topological magnons and spin excitons in twisted transition metal dichalcogenides: Mapping electron topology to spin counterpart

TL;DR

This paper theoretically explores topologically nontrivial spin excitations, including magnons and spin excitons, in twisted transition metal dichalcogenides, revealing their inheritance of electronic topology and potential for experimental detection via thermal Hall conductance.

Contribution

It uncovers the topological nature of itinerant spin excitations in tTMDs and links their topology directly to that of the underlying electrons, a novel insight in the field.

Findings

Identification of topological magnons and spin excitons in tMoTe2

Demonstration of a topological transition induced by displacement field

Prediction of step-like changes in thermal Hall conductance

Abstract

Twisted transition metal dichalcogenides (tTMDs) provide a highly tunable platform to explore the interplay between strong correlation and topology. Among them, the properties involving the charge degree of freedom have been extensively studied, while those related to spin are much less investigated. Motivated by the recent discovery of integer and fractional quantum anomalous Hall effects in tMoTe$_2$, where the flat-band ferromagnetism is one of the essential prerequisites, we investigate theoretically the spin excitations out of the flat-band ferromagnetic ground state in tMoTe$_2$. Remarkably, we identify the itinerant magnons and spin excitons with nontrivial topology. We elaborate that the topology of these itinerant spin excitations, which are described as particle-hole bound states, inherits directly from that of the underlying electrons and is essentially different from that in local spin systems. Thus, we establish a direct relationship of the topology between the many-body excitations and their fundamental constituents. We further demonstrate that by tuning the displacement field, a topological transition for both the magnon and spin exciton happens, leading to a step-like change and bifurcation in the thermal Hall conductance, which could serve as unique and compelling evidence to be tested experimentally.