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Large Tunable Thermoelectric Effects in Superconducting Spin Valves with Commercially Available Materials

Pablo Tuero1,*, Johanne Bratland Tjernshaugen2,*, Carlos Sanchez1, César Gonzalez-Ruano1,3, Yuan Lu4, Jacob Linder2,†, and Farkhad G. Aliev5,‡

  • 1Departamento Física de la Materia Condensada C-III, Universidad Autónoma de Madrid, 28049 Madrid, Spain
  • 2Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
  • 3Department of Electrical Engineering, School of Engineering (ICAI) and Institute for Research and Technology (IIT), Universidad Pontificia Comillas, Alberto Aguilera 23, 28015 Madrid, Spain
  • 4Université de Lorraine, CNRS, Institut Jean Lamour, F-54000 Nancy, France
  • 5Departamento Física de la Materia Condensada C-III, Instituto Nicolás Cabrera (INC) and Condensed Matter Physics Institute (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain

  • *These authors contributed equally to this work.
  • †Contact author: jacob.linder@ntnu.no
  • ‡Contact author: farkhad.aliev@uam.es
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PRX Energy 4, 033003 – Published 16 July, 2025

DOI: https://doi.org/10.1103/xbgg-gttc

Abstract

Recent studies have revealed magnetically controllable thermoelectric effects in superconductor/ferromagnet (S/F) structures. A tunable cryogenic thermoelectric generator needs not only a high conversion factor between electricity and heat, but also a large change in the thermoelectric output when switching the magnetic state of the device. However, the reported modifications in thermoelectric power are either minimal, involve superconductors with relatively low critical temperatures (below 1 K), or do not utilize commercially available spintronic materials. Here, we experimentally measure and numerically model thermoelectric effects in fully epitaxial ferromagnet/superconductor/ferromagnet (F/S/F) junctions based on commercially available easily grown materials, as well as their dependence on the magnetic configuration of the ferromagnetic (F) electrodes. We observe sizeable Seebeck coefficients for the parallel alignment of the F electrodes, reaching values of about 100 μV/K. Importantly, we find a decrease of the thermoelectric signal of more than an order of magnitude when switching from a parallel to an antiparallel configuration, constituting a large thermoelectric spin-valve effect. Theoretical modeling based on a self-consistent nonequilibrium Keldysh-Usadel Green’s function theory, combined with micromagnetic simulations, qualitatively reproduce the experimental findings. The thermoelectric effect is optimized when there is a large spin-dependent electron-hole asymmetry in the superconductor combined with spin-dependent transmission through the interfaces. These findings pave the way for the development of efficient and versatile cryogenic thermoelectric heat engines.

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Popular Summary

Thermoelectric cooling enables many applications, but at very low temperatures thermoelectric materials typically perform poorly. Therefore, better material platforms that yield efficient thermoelectricity under cryogenic conditions are needed. Here, the authors present experimental studies of thermoelectric effects in superconductor/ferromagnet junctions based on commercially available, easily grown materials. They observe a large Seebeck coefficient exceeding 100 microvolt/Kelvin that changes by an order of magnitude upon switching the magnetic alignment of the system. This approach paves the way for developing efficient and magnetically controllable localized cryogenic cooling.

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PRX Energy 4, 033003– Published 16 July, 2025
  • Received 24 January 2025
  • Revised 14 May 2025
  • Accepted 25 June 2025
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