Effects of Dzyaloshinskii-Moriya interactions in volborthite: Magnetic orders and thermal Hall effect

TL;DR

This paper investigates how Dzyaloshinskii-Moriya interactions influence magnetic orders and induce a thermal Hall effect in volborthite, a frustrated quantum magnet, through an effective model and comparison with experimental data.

Contribution

It introduces an effective model incorporating DM interactions in volborthite, explaining the thermal Hall effect and magnetic behavior with a quasi-one-dimensional perspective.

Findings

Magnon excitations acquire Berry curvature due to DM interactions.

The model qualitatively explains experimental magnetization and thermal Hall conductivity.

Field direction critically affects low-temperature magnetic phases.

Abstract

Volborthite offers an interesting example of a highly frustrated quantum magnet in which ferromagnetic and antiferromagnetic interactions compete on anisotropic kagome lattices. A recent density functional theory calculation has provided a magnetic model based on coupled trimers, which is consistent with a broad 1/3-magnetization plateau observed experimentally. Here we study the effects of Dzyaloshinskii-Moriya (DM) interactions in volborthite. We derive an effective model in which pseudospin-1/2 moments emerging on trimers form a network of an anisotropic triangular lattice. Using the effective model, we show that for a magnetic field perpendicular to the kagome layer, magnon excitations from the 1/3-plateau feel a Berry curvature due to the DM interactions, giving rise to a thermal Hall effect. Our magnon Bose gas theory can explain qualitative features of the magnetization and the thermal Hall conductivity measured experimentally. A further quantitative comparison with experiment poses constraints on the coupling constants in the effective model, promoting a quasi-one-dimensional picture. Based on this picture, we analyze low-temperature magnetic phase diagrams using effective field theory, and point out their crucial dependence on the field direction.