Intrinsic spin Nernst effect in topological Dirac and magnetic Weyl semimetals

TL;DR

This paper explores the intrinsic spin Nernst effect in topological Dirac and magnetic Weyl semimetals, revealing conditions for significant spin currents and potential for efficient heat-to-spin conversion in topological materials.

Contribution

It demonstrates how the intrinsic spin Nernst effect depends on Fermi energy and magnetic properties, highlighting the potential of topological semimetals for spin caloritronics applications.

Findings

Intrinsic SNE is significant near point nodes with Fermi energy deviations.

Small Fermi surface TDSMs exhibit larger spin Nernst angles than heavy metals.

Magnetic exchange coupling variations can reverse the spin Nernst current.

Abstract

We investigate the intrinsic spin Nernst effect (SNE), a transverse spin current induced by temperature gradients, in topological Dirac semimetals (TDSMs) and magnetic Weyl semimetals (MWSMs) with Ising spin-orbit coupling. The intrinsic SNE is described by the spin Berry curvature, which reflects the geometric nature of TDSMs and MWSMs. We clarified that the intrinsic SNE becomes significant when the Fermi energy is near, but slightly deviates from, the energy of the point nodes. In this situation, Bloch electrons with strong spin Berry curvature contribute to the SNE while avoiding carrier compensation between electrons and holes. We found that in TDSMs with small Fermi surfaces, the spin Nernst angle, which measures the efficiency of the SNE, is larger than that observed in heavy metals. This suggests that TDSMs with small Fermi surfaces can achieve efficient heat-to-spin current conversion. In MWSMs, variation in the magnitude of the exchange coupling with magnetic moments significantly changes the SNE, affecting both the direction and magnitude of the spin Nernst current. This implies that ferromagnetic transitions can be used to reverse the spin Nernst current. These results provide the fundamentals for future topological spin caloritronics.