Temperature dependence of the low-frequency noise properties in Bi2Sr2CaCu2Oy intrinsic Josephson junctions

We have measured the temperature dependence of the low-frequency noise properties across for mesa stacks of intrinsic Josephson junctions (IJJs) in single crystals of Bi₂Sr₂CaCu₂O_y (BSCCO) in the absence of an external magnetic field. The measured curves for noise spectrum density S_V(f) showed a 1/f frequency dependence at temperatures in the range from 4.3 K to 150 K except 36 K. We estimated the magnitude of the S_V(f) by using Rogers and Buhrman´s empirical theory and Machlup´s formula. From the observed curves for S_V(f), we estimated a 1/f noise level η for a BSCCO IJJ biased at a sub-gap voltage of approximately 10^-5 μm², and this value was almost completely independent of temperature in the range between 4.3 K and 40 K. We also found that the η values above T_c were smaller by a factor of approximately 10 than those below T_c. The η value for the BSCCO IJJ is approximately two orders of magnitude greater than for an epitaxial NbN/MgO/NbN tunnel junction biased above-gap voltage. We consider that the observed variation in the noise level with temperature is not interpretable in terms of a magnetic origin and the 1/f noise in a BSCCO IJJ may be somehow associated with stress or defects in the BiO and/or SrO layers act as tunnel barriers.