Tunneling measurements on spin-paired superconductors with spin-orbit scattering

Electron spin effects in superconducting Al films have been studied by measuring the conductance of tunnel junctions in a magnetic field. Superconductor-normal-metal tunnel junctions were made with 50-Å-thick Al and 500-1000-Å-thick Ag films with ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ as the barrier. The measured conductance curves were fit by theoretical calculations, which included depairing effects and spin-orbit scattering, and values of the depairing parameter ${\zeta }_0$ and the spin-orbit parameter $b_0$ were obtained. The relation ${\zeta }_0=\zeta \mathrm{}\left(0\right)+\frac{C H^2}{{\Delta }_0}$ was found to describe the (parallel) magnetic field dependence of the depairing. The values of $b_0$ obtained were independent of $H$. Superconductor-superconductor tunnel junctions made with two 50-Å-thick Al films were studied with various amounts of Ge and Mn impurities. The Ge impurity simply raised $T_c$, whereas the Mn lowered $T_c$ and increased $b_0$. The approximate dependence of $b_0$ on the Mn impurity concentration was obtained. The qualitative features for spin-orbit scattering predicted by theory were observed, and spin-flip scattering in the tunneling process was shown to be negligible.