1/f noise in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathit{x}}$ bicrystal grain-boundary Josephson junctions

We have measured the low-frequency 1/f voltage noise of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathit{x}}$ bicrystal grain-boundary Josephson junctions (GBJ’s). The origin of the 1/f noise are fluctuations δ${\mathit{I}}_{\mathit{c}}$ and δ${\mathit{R}}_{\mathit{n}}$ of their critical current and normal resistance, respectively. The ratio p of the normalized fluctuations ‖δ${\mathit{I}}_{\mathit{c}}$/${\mathit{I}}_{\mathit{c}}$‖/‖δ${\mathit{R}}_{\mathit{n}}$/${\mathit{R}}_{\mathit{n}}$‖ is found to be p=1.9±0.25 independent of temperature. The analysis of the noise data indicates that the critical current and resistance fluctuations are correlated. The measured noise properties can be consistently explained by the intrinsically shunted junction model based on an insulating layer at the grain boundary containing a high density of localized defect states.