Thermoelectric Measurements in Superconductor-Ferromagnet Hybrids

Superconductors are conventionally thought to be especially unsuitable as thermoelectrics since there is perfect electron hole symmetry in the quasiparticle dispersion about the Fermi energy. However, recent theoretical studies of superconductor-ferromagnet (S-F) hybrids predict a very large thermoelectric effect in these systems. If true, this would make these the only efficient cryogenic thermoelectric materials. In this work, we have developed the hardware and techniques necessary to make on-chip, thermoelectric measurements at sub 1K temperatures. We have also directly measured the Seebeck voltage in S-F structures down to 8 mK. Our measurements provide critical insights to refine theories and lay the foundation for future thermal measurements of these fascinating systems.