The thermoelectric voltage produced across a superconductor-normal metal-superconductor (SNS) sandwich by an applied heat current has been measured in Pb-Cu-PbBi and In-Al-Sn as a function of temperature. The observed divergence of the thermoelectric voltage near Tc is attributed to a charge imbalance region decaying into the superconductor from the NS interface over the quasiparticle diffusion length λQ*. The charge imbalance is generated by thermoelectrically driven quasiparticle currents in the super-conductor. It contributes a voltage per unit heat power given by Vs/P = λQ*S/κA, where A is the sample cross-sectional area, and S and κ are the thermopower and the thermal conductivity of quasiparticles in the super-conductor. For Pb and In, we find the measured thermopower in the super-conducting state to be slowly varying with temperature near Tc and consistent in magnitude with normal state values. This result is in agreement with theoretical predictions of thermoelectric effects in superconductors but contrary to previous experimental results obtained by other methods.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Materials Science(all)
- Condensed Matter Physics