Thermal Hall Effect of Spins in a Paramagnet

TL;DR

This paper develops a theoretical framework for understanding the thermal Hall effect of spins in a paramagnetic phase, linking spin chirality to Hall currents and calculating relevant coefficients using mean-field theory.

Contribution

It introduces a novel approach to derive spin Hall response functions in paramagnets by identifying the thermal Hall current operator with spin chirality and employs Schwinger boson mean-field theory for calculations.

Findings

Thermal Hall response in paramagnets can be derived from spin chirality.

Schwinger boson mean-field theory effectively calculates Hall coefficients.

Comparison with ordered phase methods highlights differences in spin transport.

Abstract

Theory of Hall transport of spins in a correlated paramagnetic phase is developed. By identifying the thermal Hall current operator in the spin language, which turns out to equal the spin chirality in the pure Heisenberg model, various response functions can be derived straightforwardly. Subsequent reduction to the Schwinger boson representation of spins allows a convenient calculation of thermal and spin Hall coefficients in the paramagnetic regime using self-consistent mean-field theory. Com- parison is made to results from the Holstein-Primakoff reduction of spin operators appropriate for ordered phases.