Strongly Coupled Spin, Heat and Charge Currents in Superconducting Hybrids
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- Institutt for fysikk 
We study the large thermoelectric effects arising as a result of strongly coupled spin, heat and charge currents in superconducting hybrids theoretically. Two new frameworks for calculating thermoelectric coefficients are presented, one including the possibility of spin-dependent bias application to homogeneously magnetized materials, and the other utilizing the quasiclassical framework allowing for spin-splitting polarizations along more than one axis. The thermoelectric coefficient governing pure thermal spin currents, the Seebeck coefficient S and the thermoelectric figure of merit ZT are all maximized when tunneling is considered to be across an insulating barrier between two Zeeman-split superconducting reservoirs. The disadvantage of such a configuration is the large external magnetic fields which need be applied for the thermoelectric effects to arise. Therefore, we here present results indicating large thermoelectric effects of similar orders of magnitude arising in superconducting hybrids wherein the particle-hole symmetry is broken without the use of large external magnetic fields. Within the low-field material systems studied, all tunneling occurs from the middle of the central layer in a Josephson junction into a normal-metal electrode. The central nanowire in the Josephson junction (i) contains spatially varying magnetization, (ii) is coupled to spin-active interfaces (such as magnetic insulators) or (iii) has intrinsic spin-orbit interaction of Rashba type.