Peculiarities of Fluxon Shift Current in a Disordered S-I-S-Tunnel Junction

When a Josephson vortex (fluxon) moves in a tunnel S-IS (S – superconductor, I – insulator) contact, in the I-layer of which there are random inhomogeneities, the radiation friction of the vortex against these inhomogeneities leads to a slowdown in its movement. To control the speed of the fluxon, a current can be introduced into the contact – the so-called fluxon shift current. In the article, the behavior of the fluxon shift current in a long S-I-S-tunnel junction with weak (low impurity concentrations) structural disorder in the I-layer is studied using a numerical-analytical method. Quantum resonant percolation trajectories (QRPTs), also called Lifshitz-Kirpichenkov trajectories, which are randomly formed in the I-layer containing impurity atoms, are considered as an inhomogeneity that influences the vortex dynamics. The fluxon shift current was considered in the parameter space (δ, c), where δ = µ − ε0 is the deviation of the Fermi level of the junction from the local single-electron impurity level. It is shown that there are physically significant concentration values at which the dependence of the shift current on δ has features (additional maxima) caused by the contributions of the QRPTs passing through different numbers of impurities. Not only quantitative but also qualitative (appearance and disappearance of features) changes in the dependence of the fluxon shift current on δ were also revealed. The results obtained can be useful in interpreting experimental data, as well as in creating technical devices based on disordered S-I-S-contacts.