Magnetic control over the superconducting thermoelectric effect

Over the past decade, it has been shown both theoretically and experimentally that a giant thermoelectric effect can arise when superconductors are coupled to strongly spin-polarized ferromagnets. The thermopower of such devices is orders of magnitude higher than metallic thermoelectric devices at comparable temperatures, and many applications of this effect have already been proposed. Here, we demonstrate a new key advantage of superconductor-ferromagnet hybrids as a platform for novel thermoelectric devices. We experimentally show that the thermopower in V/MgO/Fe/MgO/Fe/Co superconductor-spin valve hybrids (which recently revealed equal spin superconducting triplet generation due to spin-orbit coupling and symmetry filtering [1,2]) can be controlled via the relative magnetic alignment of the ferromagnetic electrodes [3]. Importantly, we confirm the theoretical prediction that by rotating one magnetic layer we can not only substantially change the thermoelectric effect, but can even reverse its sign [3,4] with an optimum antiparallel alignment of the ferromagnetic electrodes (as confirmed by the experiments and modelling). The description of the experimental results is improved by the introduction into the model of an interfacial domain wall in the spin filter layer interfacing the superconductor. Additionally, we demonstrate the in-situ control of thermoelectric effects in Fe/MgO/V/MgO/Fe/Co junctions by the relative alignment of the two ferromagnetic electrodes, in this case one at each side of the superconductor. Our results could lead to the development of a novel kind of superconducting thermoelectric generators and sensors. [1] I. Martínez, et al, Phys. Rev. Appl. 13, 014030 (2020). [2] C. González-Ruano et al., Phys. Rev. B 102 020405(R) (2020). [3] C. González-Ruano et al., Phys. Rev. Lett., 130, 237 (2023). [4] J. A. Ouassou et al., Phys. Rev. B 106, 094514 (2022).