Low-frequency noise and Hall effect measurements on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

摘要

We report 1/f noise and Hall effect measurements performed on c-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films at superconducting transition and in normal state. Magnetic fields up to 6 kG were applied parallel to c-axis. The voltage noise spectral density was normalized using Hall carrier density as well as atomic concentration. Close to the superconductive state, normalized voltage noise spectral density had a sharp rise. The noise did not seem to originate from local thermal fluctuations. We interpreted the data in terms of the classic percolation model near superconductive transition, according to which normalized noise is proportional to R/sup -k'/s/, where R is the macroscopic sample resistance and k' and s are critical exponents. The ratio k'/s, which can be regarded as an index of the rise of normalized noise, steadily increased with higher magnetic field. The zero-Gauss value of k'/s was calculated as 1.06; a result that agrees with the prediction of the classical percolation theory for a 2-D network.