Shot noise and Coulomb blockade of Andreev reflection

We derive low energy effective action for a short coherent conductor between normal (N) and superconducting (S) reservoirs. We evaluate interaction correction $\delta G$ to Andreev conductance and demonstrate a close relation between Coulomb effects and shot noise in NS systems. In the diffusive limit doubling of both shot noise power and charge of the carriers yields $|\delta G|$ four times bigger than in the normal case. Our predictions can be directly tested in future experiments.Comment: 4 pages, 2 figure

Current fluctuations in composite conductors: Beyond the second cumulant

Employing the non-linear $\sigma$-model we analyze current fluctuations in coherent composite conductors which contain a diffusive element in-between two tunnel barriers. For such systems we explicitly evaluate the frequency-dependent third current cumulant which also determines the leading Coulomb interaction correction to shot noise. Our predictions can be directly tested in future experiments.Comment: 6 pages, 1 figur

Andreev interferometer with three superconducting electrodes

We develop a quasiclassical theory of Andreev interferometers with three superconducting electrodes. Provided tunneling interface resistance between one superconducting electrode and the normal metal strongly exceeds two others, significant current sensitivity to the external magnetic flux is observed only at subgap voltages. If all barrier conductances are comparable, multiple Andreev reflection comes into play and substantial current modulation can be achieved in both subgap and overgap voltage regimes. Our analysis reveals a large variety of interesting features which can be used for performance optimization of Andreev interferometers.Comment: 9 pages, 13 figure

Electron transport and current fluctuations in short coherent conductors

Employing a real time effective action formalism we analyze electron transport and current fluctuations in comparatively short coherent conductors in the presence of electron-electron interactions. We demonstrate that, while Coulomb interaction tends to suppress electron transport, it may {\it strongly enhance} shot noise in scatterers with highly transparent conducting channels. This effect of excess noise is governed by the Coulomb gap observed in the current-voltage characteristics of such scatterers. We also analyze the frequency dispersion of higher current cumulants and emphasize a direct relation between electron-electron interaction effects and current fluctuations in disordered mesoscopic conductors.Comment: 16 pages, 4 figure

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

Josephson current in ballistic heterostructures with spin-active interfaces

We develop a general microscopic theory of dc Josephson effect in hybrid SNS structures with ballistic electrodes and spin-active NS interfaces. We establish a direct relation between the spectrum of Andreev levels and the Josephson current which contains complete information about non-trivial interplay between Andreev reflection and spin-dependent interface scattering. The system exhibits a rich structure of properties sensitive to spin-dependent barrier transmissions, spin-mixing angles, relative magnetization orientation of interfaces and the kinematic phase of scattered electrons. We analyze the current-phase relations and identify the conditions for the presence of a pi-junction state in the systems under consideration. We also analyze resonant enhancement of the supercurrent in gate-voltage-driven nanojunctions. As compared to the non-magnetic case, this effect can be strongly modified by spin-dependent scattering at NS interfaces.Comment: 11 pages, 9 figures; version published in Phys. Rev.