Skyrmions and Hall Transport

TL;DR

This paper derives Ward identities linking topological charge, such as Skyrmions, to Hall transport phenomena, providing new theoretical insights and predictions for experimental signatures in condensed matter systems.

Contribution

It introduces a generalized set of Ward identities that incorporate topological charge effects into Hall transport, extending the theoretical framework for Skyrmion-related phenomena.

Findings

Topological charge influences Hall conductivity and Hall viscosity.

Derived relations match existing experimental data.

Predicted new signatures of Skyrmions in Hall measurements.

Abstract

We derive a generalized set of Ward identities that captures the effects of topological charge on Hall transport. The Ward identities follow from the 2+1 dimensional momentum algebra, which includes a central extension proportional to the topological charge density. In the presence of topological objects like Skyrmions, we observe that the central term leads to a direct relation between the thermal Hall conductivity and the topological charge density. We extend this relation to incorporate the effects of a magnetic field and an electric current. The topological charge density produces a distinct signature in the electric Hall conductivity, which is identified in existing experimental data, and yields further novel predictions. For insulating materials with translation invariance, the Hall viscosity can be directly determined from the Skyrmion density and the thermal Hall conductivity to be measured as a function of momentum.