Spin-dependent thermoelectric transport in HgTe/CdTe quantum wells

TL;DR

This paper investigates thermally induced spin and charge transport in HgTe/CdTe quantum wells, revealing signatures of edge state gaps and deriving a relation between the spin Nernst signal and spin Hall conductance.

Contribution

It provides a detailed numerical analysis of thermoelectric effects in topological quantum wells and establishes an exact Mott-like relation for the spin Nernst signal.

Findings

Edge states show a gap signature in thermoelectric signals.

The spin Nernst signal relates to the spin Hall conductance via a Mott-like relation.

Analytical models explain the origin of transport signatures.

Abstract

We analyze thermally induced spin and charge transport in HgTe/CdTe quantum wells on the basis of the numerical non-equilibrium Green's function technique in the linear response regime. In the topologically non-trivial regime, we find a clear signature of the gap of the edge states due to their finite overlap from opposite sample boundaries -- both in the charge Seebeck and spin Nernst signal. We are able to fully understand the physical origin of the thermoelectric transport signatures of edge and bulk states based on simple analytical models. Interestingly, we derive that the spin Nernst signal is related to the spin Hall conductance by a Mott-like relation which is exact to all orders in the temperature difference between the warm and the cold reservoir.