Thermoelectric effects in superconductor-ferromagnetic heterostructures*

Superconductor-ferromagnetic (S-F) heterostructures have been predicted to show significant thermoelectric effects at cryogenic temperatures. Superconductors have a poor thermoelectric figure of merit (zT) on their own due to a symmetric density of states (DOS). In the presence of an external magnetic field, the DOS of the up and down spin states becomes asymmetric separately. A spin filtering material can then be added to detect only one of the two spin states. Previously, we reported our development of an experimental platform for the measurement of thermoelectric effects in nanoscale devices at sub-Kelvin temperatures. Here, we present our measurements of the Seebeck coefficients of superconducting, ferromagnetic, and S-F hybrid nanostructures and our progress towards direct determination of thermoelectric efficiency.