title: Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions.
abstract: Background:Thermoelectric effects result from the coupling of charge and heat transport and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron-hole symmetry, which is usually quite small in metal structures. In addition, thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime.Results:We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction.Conclusion:Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to the physics of superconductor/normal-metal microrefrigerators. The spin-dependent thermoelectric signals in the linear regime are due to the coupling of spin and heat transport, and can be used to design more efficient refrigerators.
authors.affiliation: Karlsruher Institut für Technologie (KIT), Institut für Nanotechnologie, P.O. Box 3640, D-72021 Karlsruhe, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kolenda
authors.affiliation: Department of Physics, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Machon
authors.affiliation: Karlsruher Institut für Technologie (KIT), Institut für Nanotechnologie, P.O. Box 3640, D-72021 Karlsruhe, Germany.
authors.forename: Detlef
authors.initials: D
authors.lastname: Beckmann
authors.affiliation: Department of Physics, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Belzig
keywords: spintronics, superconductor-ferromagnet hybrids, thermoelectricity