Spin Nernst and thermal Hall effects of topological triplons in quantum dimer magnets on the maple-leaf and star lattices

TL;DR

This paper theoretically investigates the topological properties of triplon excitations in quantum dimer magnets on maple leaf and star lattices, revealing novel thermal Hall effects and topological transitions influenced by interactions and magnetic fields.

Contribution

It establishes a connection between triplon and magnon topological properties on complex lattices, providing analytical expressions for thermal conductivities and classifying symmetries of the lattices.

Findings

Identification of topological triplon bands with nontrivial invariants

Analytical formulas for spin Nernst and thermal Hall conductivities

Observation of multiple topological transitions and sign reversals in thermal Hall effect

Abstract

We present a comprehensive theoretical study of the topological properties of triplon excitations in spin-1/2 dimer-singlet ground states defined on the maple leaf and star lattices. Our analysis is based on a model that includes Heisenberg interactions, Dzyaloshinskii-Moriya (DM) interactions, and an external magnetic field. In the absence of an in-plane DM vector, we demonstrate that the triplon Hamiltonian maps onto the magnon Hamiltonian of the Kagome lattice, inheriting its nontrivial topological characteristics, including Berry curvature and topological invariants such as the Z2 invariant and Chern numbers. This correspondence enables us to derive analytical expressions for the spin Nernst and thermal Hall conductivities at low temperatures. Furthermore, we explore the effects of realistic finite in-plane DM interactions, uncovering multiple topological transitions and a complex thermal Hall conductivity behavior, including potential sign reversals as functions of magnetic field and temperature. Using layer groups, we also provide a symmetry classification of the star and maple leaf lattices.