The Ginzburg-Landau parameter in the case of non-pure superconductors

The concept of the Ginzburg-Landau parameter, κ, and of its extension to the case of non-pure materials is discussed in the framework of the BCS formulation and of the boson formulation. The data derived from several experiments performed on different samples containing various concentrations of scalar impurities are analyzed. We find that the value of κ for pure Ta, Nb and V is 0.350, 0.778 and 0.802, respectively. The theoretical dependence of κ by the electron mean free path is compared with the experimental behavior.