DEEP PINNING CENTERS IN BI-SR-CA-CU-O THIN-FILMS AT WEAK MAGNETIC-FIELDS

Pinning centres in c-axis oriented Bi - Sr - Ca - Cu - O thin films have been investigated, using a new technique relying on measurements of low frequency voltage noise in the d.c. current and d.c. magnetic field biased superconducting strips. Random telegraph voltage signals arising from single flux jumps between two pinning sites have been observed at temperatures close to T(c) and in weak magnetic fields below 10 G. The thermally activated behaviour of the average lifetimes, with activation energies of the order of 420 meV and attempt rates of the order of 10(6) Hz, has been estimated from the temperature and magnetic field dependence of the noise waveforms. Experimental evidence has been found for the xi2 scaling of the pinning volume that enabled the determination of the exact functional form of the temperature and the magnetic field dependence of the pinning energy in the samples.