Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures

Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V approximate to 2 Delta/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2 Delta/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3699014]