Rashba-driven anomalous Nernst conductivity of lead chalcogenide films

Abstract

The presence of a finite Berry curvature $\left(\Omega\left(k\right)\right)$ leads to anomalous thermal effects. In this letter, we compute the coefficients for the anomalous Nernst effect $\left(ANE\right) $ and its spin analogue, the spin Nernst effect $\left(SNE\right)$ in lead chalcogenide (\textit{PbX}; \textit{X} = S, Se, Te) films. The narrow gapped \textit{PbX} films with a large spin-orbit coupling (\textit{soc}) offer a significant Rashba interaction that gives rise to $ \Omega\left(k\right) $ and the attendant anomalous thermal behaviour. In presence of a temperature gradient, the $ ANE $ and $ SNE $ establish a thermal and spin current and are characterized by their respective coefficients which acquire higher values for a stronger Rashba interaction. We further show that an extrinsic \textit{soc} generated by an in-plane electric field offers a gate-like mechanism to control (and turn-off) the anomalous thermal currents. Finally, we conclude by deriving the efficiency of an $ ANE $-driven low-temperature Carnot heat engine and demonstrate that it can be gainfully optimized in systems with a robust intrinsic \textit{soc} resulting in low carrier effective masses.