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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. ; This research was supported by MINECO under Grant No. FIS2011-23526, the Kavli Institute for Theoretical Physics through NSF Grant No. PHY11-25915 and the National Research Foundation of Korea (NRF) grants funded by the Korea government (MSIP) (Grant No. 2011-0030046). ; Peer Reviewed

Nonlinear transport coefficients do not obey, in general, reciprocity relations. We here discuss the magnetic-field asymmetries that arise in thermoelectric and heat transport of mesoscopic systems. Based on a scattering theory of weakly nonlinear transport, we analyze the leading-order symmetry parameters in terms of the screening potential response to either voltage or temperature shifts. We apply our general results to a quantum Hall antidot system. Interestingly, we find that certain symmetry parameters show a dependence on the measurement configuration. © IOP Publishing and Deutsche Physikalische Gesellschaft. ; SYH and ML were supported by the National Research Foundation (NRF) grant funded by the Korea government (MSIP) (no. 2011-0030046). DS and RL were supported by MINECO grant no. FIS2011-2352. ; Peer Reviewed

We propose a two-terminal spin-orbit interferometer with a hot molecule inserted in one of its arms to generate pure spin currents. Local heating is achieved by coupling the vibrational modes of the molecule to a third (phononic) reservoir. We show that this spin caloritronic effect is due to the combined influence of spin-dependent wave interference and inelastic scattering. Remarkably, the device converts heat flow into spin-polarized current even without applying any voltage or temperature difference to the electronic terminals. © 2013 AIP Publishing LLC. ; The authors acknowledge the support from MECD under Grant Nos. FIS2011-23526 and CSD2007-00042 (CPAN), and the National Research Foundation (NRF) grant funded by the Korea government (MSIP) (No. 2011-0030046). ; Peer Reviewed