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/ of films with various thicknesses (25 80), estimated from magnetoresistance data above Tc, is well fitted to a function of C0+C1T+C3T3. The coefficient C1 is in excellent quantitative agreement with the theoretical prediction of the electron-electron scattering mechanism for two-dimensional dirty metals. The coefficient C3 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.