Anomalous Thermal Hall Effect in an Insulating van der Waals Magnet VI3

TL;DR

This paper reports the discovery of an anomalous thermal Hall effect in the insulating 2D ferromagnet VI3, revealing dual magnon and phonon contributions and highlighting its potential for spintronics applications.

Contribution

It is the first ferromagnetic system to demonstrate both anomalous magnon and phonon thermal Hall effects, supported by theoretical calculations.

Findings

Thermal Hall signal persists without external magnetic field.

Sign of the thermal Hall effect flips with magnetization switching.

Dual nature of the effect dominated by magnons at high temperatures and phonons at low temperatures.

Abstract

Two-dimensional (2D) van der Waals (vdW) magnets have been a fertile playground for the discovery and exploration of physical phenomena and new physics. In this Letter, we report the observation of an anomalous thermal Hall effect (THE) with \k{appa}_xy ~ 1x10^(-2) W K^(-1) m^(-1) in an insulating van der Waals ferromagnet VI3. The thermal Hall signal persists in the absence of an external magnetic field and flips sign upon the switching of the magnetization. In combination with theoretical calculations, we show that VI3 exhibits a dual nature of the THE, i.e., dominated by topological magnons hosted by the ferromagnetic honeycomb lattice at higher temperatures and by phonons induced by the magnon-phonon coupling at lower temperatures. Our results not only position VI3 as the first ferromagnetic system to investigate both anomalous magnon and phonon THEs, but also render it as a potential platform for spintronics/magnonics applications.