DEPENDENCE OF THE 2ND-UPPER CRITICAL-FIELD ON COUPLING STRENGTH

We have calculated the second upper critical magnetic field Hc2(T) in the clean and dirty limit for a number of known strong-coupling superconductors based on tunneling-derived kernels. The microscopic theory is used to derive a simple semiphenomenological analytic form for the strong-coupling corrections that involve the single parameter Tc/ln, namely the ratio of critical temperature (Tc) to characteristic phonon energy (ln). The parameters in the derived form are fixed through consideration of our numerical data for real materials. © 1990 The American Physical Society.