Non-Thermally Activated Noise Power Spectral Density In Yba2cu3o7-Delta Thin Films

The low-frequency noise power spectral density (PSD) of highly c-axis oriented YBa2Cu3O7-delta thin-film microbridges is measured in the temperature range 77-300 K. At room temperature, the value of the Hooge parameter, gamma, is 1.8 x 10(-3), which is in the range of ordinary metal films. In the normal state, the noise PSD shows the generic '1/f noise' behaviour and decreases as the temperature is decreased. The experimental data obtained in the normal state cannot be described reasonably well by Dutta-Horn's thermally activated model. Moreover, in the transition temperature (T-c) region, the noise PSD shows 1/f(alpha) behaviour with alpha > 1 and a noise peak appears. The noise increment in the T-c region can be explained by dimensional crossover in this novel percolation noise effect.