Experimental study of thermoelectricity in superconducting indium

This paper reports on a comprehensive study of thermoelectricity in pure superconducting indium near the transition temperature. The samples consisted of hollow bimetallic toroids of lead and indium. Upon application of a temperature gradient, a magnetic flux was produced within the hollow cavity of the toroids which could be coupled, via a superconducting flux transformer, into a superconducting quantum interference device magnetometer. The thermoelectric origins of the magnetic flux and the experimental method are discussed in detail. The magnetic flux was measured in seven specimens, and in each was found to diverge as the transition temperature was approached with a ${(1-\frac{T}{T_c})}^{-\frac{3}{2}}$ power-law dependence. The magnitude of the flux varied by about a factor of 40 among the different samples and appeared to scale with the normal-state thermoelectric properties of the indium. Tests intended to eliminate possible spurious causes for the magnetic flux are also discussed.