Self-field effects on critical current density and current-voltage characteristics in superconducting YBaCuO thick films

The self-field and percolative influences on transport measurements of poly crystalline bridges engraved on YBaCuO thick film have been investigated. A maximum in the dependence of the critical current density on cross-section al area of the bridge (A = 0.003 mm(2)-0.3 mm(2)) has been found experiment ally, in samples with low critical current densities (J(c) < 50 A cm(-2)). The result of the measurements are in agreement with Mulet and coworkers, w ho have predicted that, under certain conditions, the self-field effects on transport measurements are negligible and the J(c) dependence on the sampl e dimensions is determined by the percolative character of the transport cu rrent. Self-field influences have also been observed in current-voltage cha racteristics, which have been analysed using the Ambegaokar-Halperin phase- slip theory. By allowing the noise parameter (gamma) to change with tempera ture, magnetic field and transport current, adequate agreement between theo retical and experimental current-voltage characteristics has been obtained. The dependence of the noise parameter with the transport current is demons trated to be related with the self-field.