Dynamical properties of high-temperature-superconductor granular bridge junctions: Inhomogeneous Josephson-junction-array model

As an attempt to understand the dynamical behavior of the high-temperature-superconductor (HTSC) granular bridge junction, we model the granular HTSC bridge junction consisting of many small grains inside by an inhomogeneous Josephson junction array, i.e., randomly arranged Josephson junction arrays (JJA). To describe randomly distributed critical currents between the grains inside the HTSC granular bridge junction, we chose various possible configurations in {Iijc} and {Rij} for the one-dimensional (1D) and 2D inhomogeneous Josephson junctions, and calculated the current-voltage (IV) characteristics and self-radiation spectral densities of the 1D and 2D inhomogeneous Josephson junctions. As a result, depending upon the distribution of critical currents and shunted resistances, it is found that there are large variations of IV characteristics. In contrast to the appearance of giant Shapiro steps in the regular ordered array, such Shapiro steps disappear in the case of the disordered JJA due to the increased randomness in the distribution of critical currents. On the contrary, however, when there exists a correlation between critical currents and resistances, i.e., a constant Josephson voltage, IijcRij=VJ (constant), the fundamental Shapiro step emerges despite the disordered distribution of Iijc. The relevance of this model to the HTSC granular bridge junctions is discussed. In particular, experimentally observed dynamical behaviors of the HTSC granular bridge junctions are shown to be closely related to the case of the correlated distribution with constant Josephson voltage. copyright 1996 The American Physical Society