On the energy gap in superconducting tin

Abstract

The surface resistance of specimens of superconducting tin and of tin-indium alloys has been measured at a frequency of 140 kmc/s and at temperatures near to the superconducting transition. In both single crystal and polycrystalline alloy specimens, the onset of quantum absorption was well defined and corresponded to an isotropic energy gap with a value at absolute zero of about 3·6 kT c . With pure tin, however, the absorption edge was not well defined in specimens oriented away from the tetrad axis; but near to the tetrad axis, there seems to be a considerable region in which the gap varies com paratively slowly, taking a value of about 3·6 kT c . Assuming that the absence of a clearly defined absorption edge for other orientations is the result of gap anisotropy, it is shown that regions in which the gap takes values very different from 3·6 kT c must lie well away from the tetrad axis. The analysis also shows that such regions are comparatively unimportant, and that the 3·6 kT c gap predominates strongly.