Nonlinear spin-thermoelectric transport in two-dimensional topological insulators

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.

Finding the quantum thermoelectric with maximal efficiency and minimal entropy production at given power output

“…Linear-response examples include Refs. [5,[46][47][48][55][56][57][58][59][60][61][62][63][64][65][66], while nonlinear responses were considered in Refs. [17,18,36,37,54,[67][68][69][70][71], see Refs.…”

Nonequilibrium spin-polarized thermal transport in ferromagnetic–quantum dot–metal system

“…The excess charge is piled up inside the QD due to the presence of θ α and V α . Meanwhile, the electrostatic potential U [9,22,36] is generated inside the QD. For simplicity, we assume that the Fermi level E F is zero, and the electrostatic potential is zero at the equilibrium state (eq: V α = 0 and θ α = 0), U eq = 0.…”

“…The nonlinear spin-polarization effect could be generated in two-dimensional topological insulators. Interestingly, the screening potential at the dot region becomes spin-dependent due to the voltage or temperature shifts [36]. The characteristic of the spin-polarized electron transport in the nonlinear and linear regime was described by applying an external magnetic field in the Kondo regime using higher-order Green's function in the equation of motion and numerical renormalization group method [30][31][32][33][34].…”

Transport in quantum spin Hall edges in contact to a quantum dot

“…The coupling of helical edge states to quantum dots and magnetic impurities has been addressed in several works. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] A crucial ingredient for a net resistive…”