Nonlinear spin-thermoelectric transport in two-dimensional topological insulators

TL;DR

This paper explores nonlinear spin-thermoelectric transport in two-dimensional topological insulators, revealing spin-polarized currents and heat flows driven by interactions without external magnetic fields, with potential for thermoelectric spin control.

Contribution

It demonstrates that spin polarization of charge and heat currents can be achieved purely through interactions in a quantum spin Hall antidot system, without magnetic fields or ferromagnetic contacts.

Findings

Spin-polarized electric current can be tuned via dot level and temperature.

Pure spin currents can be generated thermoelectrically with zero charge current.

Heat transport exhibits spin polarization asymmetric to bias direction.

Abstract

We consider spin-polarized transport in a quantum spin Hall antidot system coupled to normal leads. Due to the helical nature of the conducting edge states, the screening potential at the dot region becomes spin dependent without external magnetic fields nor ferromagnetic contacts. Therefore, the electric current due to voltage or temperature differences becomes spin polarized, its degree of polarization being tuned with the dot level position or the base temperature. This spin-filter effect arises in the nonlinear transport regime only and has a purely interaction origin. Likewise, we find a spin polarization of the heat current which is asymmetric with respect to the bias direction. Interestingly, our results show that a pure spin current can be generated by thermoelectric means: when a temperature gradient is applied, the created thermovoltage (Seebeck effect) induces a spin-polarized current for vanishingly small charge current. An analogous effect can be observed for the heat transport: a pure spin heat flows in response to a voltage shift even if the thermal current is zero.