Rules for the Energy Gap and Critical Field of Superconductors

Abstract

Two simple empirical rules are given by which to characterize the energy gap and critical field of most superconductors: for the reduced energy gap $\ensuremath{\delta}$, ${[\frac{\ensuremath{\Delta}(T)}{\ensuremath{\Delta}(0)}]}^{2}\ensuremath{\equiv}{\ensuremath{\delta}}^{2}=cos(\frac{\ensuremath{\pi}{t}^{2}}{2}),$ where $t=\frac{T}{{T}_{c}}$; and for the reduced critical field $h$, $h+{D}_{0}sin\ensuremath{\pi}h=1\ensuremath{-}{t}^{2},$ where ${D}_{0}$ is the maximum deviation from a parabola. An improved method of extrapolating critical-field data to 0\ifmmode^\circ\else\textdegree\fi{}K is described.