Flux origin of random telegraph voltage signals in high-t_c superconducting thin films

Random telegraph voltage noise signals strongly dependent on externally applied magnetic field and transport current have been detected in c-axis-oriented BiSrCaCuO thin films at temperatures just below the onset of superconductivity. Signals appeared only in a narrow range of bias currents and associated magnetic fields. Such signals, already observed in granular YBaCuO films at helium temperatures, seem to be a universal feature of high-T_c superconducting films. Observed signals are consistently interpreted as an evidence of vortex hopping between two distinct pinning sites. Resistivity fluctuations and intrinsic SQUID detection are proposed as alternative mechanisms converting flux noise into random telegraph voltage signals.