Emission from a Stack of Josephson Junctions with Gaussian Spread of Critical Currents

Abstract

IV-characteristics and ac power of emission were calculated for the model of the stack of two long Josephson junctions with inductive coupling. Distributions of critical currents along junctions had Gaussian spread. Zero-field steps at averaged voltages which correspond to frequencies of in-phase modes of oscillations of voltages over junctions as well as maxima of ac power of emission at these steps were found. The dependence of ac power on the value of spread was investigated in the hysteretic region at the backward movement of the bias current. We found that coherent emission existed at large Gaussian spread of critical currents (up to 30%). We believe that such strong synchronization of voltage oscillations of junctions in the stack appears due to the influence of strong ac currents in neighbor segments of junctions. These currents come into existence due to inequality of critical currents of segments. Strong ac currents synchronize oscillations of voltages across segments of long junctions in the whole stack, increase the tolerant spread of critical currents and lead to strong phase locking.