KOSTERLITZ-THOULESS TRANSITION AND CONDUCTIVITY FLUCTUATIONS IN Y-BA-CU-O THIN-FILMS

Kosterlitz-Thouless properties of c-axis-oriented high-Tc superconducting YBa2Cu3O7-x thin films were examined. The current-voltage characteristics over a wide current range obeyed a power-law relationship. The exponent (T) showed a universal jump at Tc. The exponential inverse-square-root reduced-temperature dependence of the resistance above Tc was consistent with a two-dimensional (2D) behavior of the thin films. Excess conductivity due to thermal fluctuations of the order parameter above the mean-field transition temperature Tc0 was also measured. However, the paraconductivity showed a 1D-like behavior at temperatures close to Tc0 and further complications at higher temperatures. This 1D-like behavior could be the result of imperfections of the dimensionality of 2 in the polycrystalline sample. © 1990 The American Physical Society.