Weak localization, fluctuation, and superconductivity in thin Nb films and wires

Weak localization, fluctuation conductivity, and related problems have been investigated based on a comprehensive set of experiments on transition metal Nb films and wires. The temperature dependence of the inelastic scattering rate 1/τ_φ of films with various thicknesses (25--80 {}), estimated from magnetoresistance data above Tc, is well fitted to a function of C₀+C₁T+C₃{T}³$. The coefficient ${C}₁$ is in excellent quantitative agreement with the theoretical prediction of the electron-electron scattering mechanism for two-dimensional dirty metals. The coefficient ${C}₃$ shows no thickness dependence and is in semiquantitative agreement with theories of three-dimensional electron-phonon scattering mechanisms. The upper critical field of thin Nb wires with a width of less than 1000 {} exhibits unconventional temperature dependence close to Tc. We also discuss this behavior.