Anomalous Nernst and Righi-Leduc effects in Mn${}_3$Sn: Berry curvature and entropy flow

Abstract

We present a study of electric, thermal and thermoelectric response in noncollinear antiferromagnet Mn${}_3$Sn, which hosts a large Anomalous Hall Effect (AHE). Berry curvature generates off-diagonal thermal(Righi-Leduc) and thermoelectric(Nernst) signals, which are detectable at room temperature and invertible with a small magnetic field. The thermal and electrical Hall conductivities respect the Wiedemann-Franz law, implying that the transverse currents induced by Berry curvature are carried by Fermi surface quasi-particles. In contrast to conventional ferromagnets, the anomalous Lorenz number remains close to the Sommerfeld number over the whole temperature range of study, excluding any contribution by inelastic scattering and pointing to Berry curvature as the unique source of AHE. The anomalous off-diagonal thermo-electric and Hall conductivities are strongly temperature-dependent and their ratio is close to k${}_B$/e.

main text (5 pages, 4 figures) includes supplement, to appear in Phys. Rev. Lett