Thermoelectrostatic effects in superconductors

This experiment was undertaken in order to investigate the possible existence of a thermoelectrostatic effect in superconductors which is predicted on the basis of the two-fluid London model of superconductivity and an analogy with superfluid helium II. The phenomenon of Josephson tunneling is used as a means of detecting such an effect since any thermally generated supercurrent should produce a shift in the critical current of a Josephson point contact. Niobium was chosen as the sample because of its good mechanical properties and high predicted thermopower. Samples were prepared at ultrahigh vacuum (10-10 Torr) and 4.2 K to prevent surface contamination. Contrary to the results of two previous experiments, these measurements show that, within the limitations of the data collection system, no thermoelectrostatic effect exists in Nb which implies that no such effect exists in any superconductor. An upper limit more than one order of magnitude smaller than the predicted value can be placed on this effect