Nonequilibrium Josephson-like effects in wide mesoscopic SNS junctions

Abstract

Mesoscopic superconducting-normal-metal-superconducting (S-N-S) junctions with a large separation between the superconducting electrodes (i.e. wide junctions) exhibit nonequilibrium supercurrents, even at temperatures for which the equilibrium Josephson effect is exponentially small. The second harmonic of the Josephson frequency dominates these currents, as observed in recent experiments. A simple description of these effects, in the spirit of the Resistively-Shunted-Junction model, is suggested here. It is used to calculate dc I-V characteristics, and to examine the effects of various types of noise and of external microwave radiation (Shapiro steps). It is found that the nonequilibrium supercurrents are excited when the junction is driven by a dc bias or an ac bias, or even by external noise. In the case of junctions which are also long in the direction perpendicular to the current flow, thermodynamic phase fluctuations (thermal noise) alone can drive the quasiparticles out of local equilibrium. Magnetic flux is then predicted to be trapped in units of Φ0/2 = hc/4e.

Subgap structure in the conductance of a three-terminal Josephson junction

“…In that case, the second harmonic response obtained by Argaman et al [33] in the case of a two terminal SNS junctions, transposes into a response at a frequency ν a + ν b giving rise to DC features when ν a = −ν b .…”

“…Such a problem indeed reminds the one considered in Refs. [25,33,34]. In a clean SNS junction polarized with a voltage V , oscillations with a frequency double of the basic Josephson frequency ω = 2eV h are generated and show up under microwave irradiation as halfinteger Shapiro steps.…”

“…In a clean SNS junction polarized with a voltage V , oscillations with a frequency double of the basic Josephson frequency ω = 2eV h are generated and show up under microwave irradiation as halfinteger Shapiro steps. This was explained by Argaman [33] within a semi-phenomenological description in which the both the Andreev levels and their steady state distribution oscillate at the Josephson frequency. The argument applies in the adiabatic regime in which the Thouless energy is much larger than the applied voltage.…”

“…[25,33,34], e.g. that the voltage is small enough to allow an adiabatic approximation both in the current components and in the Andreev state distribution.…”

Admittance of a long diffusive SNS junction

“…In our work, we concentrate on how this rich physics shows itself in the linear response function Y . Since Lempitskii's work, there was not much theoretical activity on the coherent contribution to Y with notable exceptions provided by 23,24 . However, the recent experiments motivated a series of theoretical studies 11,25,26 .…”