T4 to T2 resistivity transition and superconducting fluctuations in disordered VN films.

Thin films of Vn have been prepared with a wide range of structural disorder as characterized by residual resistivities from the clean value of rho/sub 0/ = 5.0 ..mu cap omega.. cm up to 100 ..mu cap omega.. cm. The disorder is primarily a consequence of nitrogen vacancies in as-made films or ..cap alpha..-particle damage of clean, stoichiometric VN. We have observed a transition in the power-law dependence of the low-temperature resistivity from T/sup 4/ to T/sup 2/ as disorder increases, consistent with the universal behavior of strong-coupled superconductors proposed by Gurvitch. Comparison of this transition with the universal plot leads to an estimate of the electron-phonon coupling lambda/sub p/ between 1.0 and 1.1. Disordered films also display an enhanced conductivity several degrees above T/sub c/ which is well described by a model of three-dimensional (3D) superconducting fluctuations. This represents one of the few cases where fluctuation enhanced conductivity has been observed in 3D films, other cases being the high-T/sub c/ oxides such as YBa/sub 2/Cu/sub 3/O/sub 7/.