The thermal resistance of tin-indium alloys in the intermediate state

Abstract

The thermal conductivity and magnetic moment of several Sn-In alloys have been measured during the destruction of superconductivity by a transverse magnetic field. The alloys contained from 2 to 8% In and were examined in the range from about 2 °K to the transition temperature T c . The samples with less than 4 or 5% In show the maxima in the intermediate state thermal resistivity which have been observed by many authors in the case of pure metals. The temperature dependence of the ‘additional resistivity’, w a , deduced from the maxima varies with impurity and does not agree in any case with the results on pure metals. A simple extension of existing theory shows, however, that the discrepancy is due to a large contribution to w a by phonon scattering at laminar boundaries. The laminar period, z , is deduced and is shown to decrease with increasing impurity concentration. For indium concentrations larger than 4 or 5% the maxima vanish. This is shown to occur when the electronic mean free path l en ~ λ, the penetration depth, where the magnetic momenta data indicate that large superconducting regions can be stable in fields greater than H c . The disappearance of w a is attributed to z ≪ l gs , the phonon mean free path, and z ~ l en under these conditions.