Elementary and macroscopic two-level fluctuations in high-T_c superconductors

The relation between random telegraph noise and 1/f-type background voltage fluctuations in current biased high-T_c films has been investigated. The experiments have revealed that the telegraph noise in high-T_c superconducting films is due to a combined action of a macroscopic two-level fluctuator and a detector. The macroscopic telegraph signal does not constitute an elementary contribution to 1/f noise. However, the behavior of telegraph and 1/f-like voltage fluctuations have shown astonishing similarities. Telegraph voltage amplitudes and 1/f power spectrum magnitude scale linearly with changing current flow above almost identical threshold currents. The telegraph signal symmetry characteristics have been found to be linear also but with distinctively different offset currents. Analysis of the measured characteristics indicates that the telegraph and 1/f fluctuations are due to different flux fluctuators coupled to observable voltages by the same detector mechanism.