抄録
The superconducting properties of Ta-rich Ta–Nb alloys have been investigated by magnetization measurements. The Ginzburg-Landau parameter κ of pure tantalum is estimated to be 0.42 and the critical value κ=1⁄\sqrt2 is attained at a composition Ta-2.4 at. % Nb. The dependence of the thermodynamic critical field on temperature T follows the BCS prediction and all the alloys are considered to be weak-coupling superconductors. The lower critical field accords with the microscopic theory in the vicinity of the transition temperature Tc, but the discrepancy between experiment and theory increases with decreasing T. The temperature dependence of the upper critical field and the generalized Ginzburg-Landau parameter κ2 is stronger than the prediction and the disparity becomes large as the electron mean free path l increases. These properties may be ascribed to the effect of the anisotropy of the electronic structure in the state where the electron mean free path l is considerably larger than the intrinsic coherence length ξ0.
