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 polycrystalline bridges engraved on YBaCuO thick film have been investigated. A maximum in the dependence of the critical current density on cross-sectional area of the bridge (A = 0.003 mm2-0.3 mm2) has been found experimentally, in samples with low critical current densities (Jc<50 A cm-2). The result of the measurements are in agreement with Mulet and coworkers, who have predicted that, under certain conditions, the self-field effects on transport measurements are negligible and the Jc dependence on the sample dimensions is determined by the percolative character of the transport current. Self-field influences have also been observed in current-voltage characteristics, which have been analysed using the Ambegaokar-Halperin phase-slip theory. By allowing the noise parameter () to change with temperature, magnetic field and transport current, adequate agreement between theoretical and experimental current-voltage characteristics has been obtained. The dependence of the noise parameter with the transport current is demonstrated to be related with the self-field.