Fluctuations of the Josephson current and electron-electron interactions in superconducting weak links

We derive a microscopic effective action for superconducting contacts with arbitrary transmission distribution of conducting channels. Provided fluctuations of the Josephson phase remain sufficiently small our formalism allows to fully describe fluctuation and interaction effects in such systems. As compared to the well studied tunneling limit our analysis yields a number of qualitatively new features which occur due to the presence of subgap Andreev bound states in the system. We investigate the equilibrium supercurrent noise and evaluate the electron-electron interaction correction to the Josephson current across superconducting contacts. At T=0 this correction is found to vanish for fully transparent contacts indicating the absence of Coulomb effects in this limit.Comment: 12 pages, 4 figure

Current-biased Andreev interferometer

We theoretically investigate the behavior of Andreev interferometers with three superconducting electrodes in the current-biased regime. Our analysis allows to predict a number of interesting features of such devices, such as both hysteretic and non-hysteretic behavior, negative magnetoresistance and two different sets of singularities of the differential resistance at subgap voltages. In the non-hysteretic regime we find a pronounced voltage modulation with the magnetic flux which can be used for improving sensitivity of Andreev interferometers.Comment: 7 pages, 7 figure

Non-local Andreev reflection under ac bias

We theoretically analyze non-local electron transport in multi-terminal normal-metal-superconductor-normal-metal (NSN) devices in the presence of an external ac voltage bias. Our analysis reveals a number of interesting effects, such as, e.g., photon-assisted violation of balance between crossed Andreev reflection (CAR) and elastic cotunneling (EC). We demonstrate that at sufficiently small (typically subgap) frequencies of an external ac signal and at low temperatures the non-local conductance of the NSN device turns negative implying that in this regime CAR contribution to the non-local current dominates over that of EC. Our predictions can be directly tested in future experiments.Comment: published version, 6 pages, 3 figure

Triplet superconductivity in a ferromagnetic vortex

We argue that odd-frequency triplet superconductivity can be conveniently realized in hybrid superconductor-ferromagnet (SF) structures with a ferromagnetic vortex. We demonstrate that due to proximity-induced long-range triplet pairing such SFS junctions can sustain appreciable supercurrent which can be directly measured in experiments.Comment: 4 pages, 3 figure