Rules for the Energy Gap and Critical Field of Superconductors

Two simple empirical rules are given by which to characterize the energy gap and critical field of most superconductors: for the reduced energy gap $\delta$, ${\left[\frac{\Delta \mathrm{}\left(T\right)\mathrm{}}{\Delta \mathrm{}\left(0\right)\mathrm{}}\right]}^2\equiv {\delta }^2=cos\left(\frac{\pi t^2}{2}\right),$ where $t=\frac{T}{T_c}$; and for the reduced critical field $h$, $h+D_{0}sin\pi h=1-t^2,$ where $D_0$ is the maximum deviation from a parabola. An improved method of extrapolating critical-field data to 0°K is described.