Inductive transition of niobium and tantalum in the 10-MHz range. I. Zero-field superconducting penetration depth

Abstract

The inductive transition of superconducting Nb and Ta was investigated at 15 MHz. These measurements provide values of ${\ensuremath{\lambda}}_{L}(0)$ for both Nb and Ta which are compared with other work. Particular attention has been given to impurities at the metal surfaces, and to how $\ensuremath{\lambda}$ is affected through a change in the boundary condition on the Ginzburg-Landau order parameter. We emphasize that in accurate measurements the surface must be characterized by a parameter describing the slope of the order parameter at the surface. A peak in the inductive skin depth has been observed in the region very close to ${T}_{c}$, where $\ensuremath{\lambda}>\ensuremath{\delta}$, and this allows ${T}_{c}$ to be determined very precisely.