Thermal fluctuations in Y-Ba-Cu-O thin films near the transition temperature

Detailed studies on the properties of low frequency noise in Y-Ba-Cu-O thin films in the transition region were conducted. Our experimental results showed that the low frequency excess noise exhibited a lower cutoff frequency of about 5 Hz, below which the noise power spectra were independent of frequency. At T close to T_C and at small current biases the voltage noise power spectra were proportional to I², (∂R/∂T)² and inversely proportional to the volume of the device, Ω. In addition, low frequency noise measured from two segments separated by a distance of 300 μm was found to be correlated. The lower cutoff frequencies computed for both the noise power spectra and the frequency dependent correlation function, according to the thermal fluctuation model, were found to be in good agreement with the experimental values. The experimental results provide strong evidence that the low frequency excess noise in the device originates from equilibrium temperature fluctuations for small T and T≃T_C