FLICKER NOISE IN YBA2CU3O7-DELTA BICRYSTAL GRAIN-BOUNDARY JUNCTIONS IN WEAK MAGNETIC-FIELDS

Flicker noise in c-axis oriented long YBCO bicrystal grain boundary ju nctions was characterized as a function of temperature, biasing condit ions, and magnetic field applied perpendicular to the a-b plane over a wide range of temperatures from 15 K to over 70 K. Aperiodic variatio ns, as a function of magnetic field, were observed in both the junctio n voltages, V-J, and the flicker noise magnitude under constant curren t bias as the magnetic field was scanned from 0 to 8 G. The noise magn itudes were found to peak at the minima of V-J. Analyses of the field dependencies of the: magnitudes and the functional form of the voltage noise power spectra show that the noise did not arise from thermally activated flux motion. Based on the dependencies of the noise power sp ectra on the bias current and the dynamic resistance of the junction, we conclude that the noise originates from the fluctuations of the cri tical current of the devices most likely due to trapping of carriers o r defect motion within the grain boundary. (C) 1995 American Institute of Physics.