Resistive noise of YBCO high-T_c granular superconductors in magnetic field

Resistance and resistance-noise experimental results, obtained in the transition region of two YBCO bulk superconductors submitted to a DC magnetic field are reported. The magnetic field was found to influence only the second stage of the transition, enlarging the transition-temperature interval and determining a shift of the noise peak towards lower temperatures. The sample is modelled as a precolating network formed by Josephson junctions and resistance noise is ascribed to the random switching of certain junctions (p-noise) [L.B. Kiss et al. Physica C 207(1993)318]. A junction may be enable to switch either by thermal fluctuations or by random motion of intergranular vortices. The square of the temperature derivative of the resistance was used to control the thermal-fluctuations effect in producing the noise. The magnetic field is believed to influence the resistance and resistance noise via a parameter p (percentage of phase-locked junctions) and p-noise behavior is considered an intrinsic property of the network.