Temperature dependence of the low-frequency noise properties in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ intrinsic Josephson junctions

Abstract

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 Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (BSCCO) in the absence of an external magnetic field. The measured curves for noise spectrum density S/sub 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/sub V/(f) by using Rogers and Buhrman's empirical theory and Machlup's formula. From the observed curves for S/sub V/(f), we estimated a 1/f noise level /spl eta/ for a BSCCO IJJ biased at a sub-gap voltage of approximately 10/sup -5/ /spl mu/m/sup 2/, and this value was almost completely independent of temperature in the range between 4.3 K and 40 K. We also found that the /spl eta/ values above T/sub c/ were smaller by a factor of approximately 10 than those below T/sub c/. The /spl eta/ 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.