Spreads in Critical Current and Normal Conductance of High- $T_{\rm c}$ dc SQUID

The statistical behaviors of the critical current (I _c) and the normal conductance (G _n) of high-T _c dc SQUIDs were investigated theoretically and experimentally. The voltage-current and voltage-flux characteristics of 38 SQUIDs fabricated on a chip were measured by using a switching-channel cryostat, which can characterize up to 43 elements individually in a series array. It was found that the spatial correlation in I _c between the neighboring SQUIDs is low, which implies that the critical current can be taken as a spatially independent random variable. The I _c and G _n histograms follow the gamma distributions. In addition, the statistical linear correlation between lnI _c and lnG _n is 0.6, which suggests that the I _c spread is partly originated from the variation in local oxygen content of bicrystal junctions.