Artem V. Galaktionov

Quantum interference and supercurrent in multiple-barrier proximity structures

We analyze an interplay between the proximity effect and quantum interference of electrons in the hybrid structures superconductor-normal-metal-superconductor which contain several insulating barriers. We demonstrate thatthe de Josephson current in these structures may change qualitatively due to quantum interference of electrons scattered at different interfaces. In junctions with few conducting channels mesoscopic fluctuations of the supercurrent are significant and its amplitude can be strongly enhanced due to resonant effects. In the many-channel limit averaging over the scattering phase effectively suppresses interference effects for systems with two insulating barriers. In that case a standard quasiclassical approach describing scattering at interfaces by means of Zaitsev boundary conditions allows us to reproduce the correct results. However, in systems with three or more barriers the latter approach fails even in the many-channel limit. In such systems interference effects remain important in this limit as well. For short junctions these effects result in additional suppression of the Josephson critical current, indicating the tendency of the system towards localization. For relatively long junctions interference effects may-on the contrary-enhance the supercurrent with respect to the case of independent barriers.

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 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. Our results illustrate a direct relation between electron-electron interaction effects and current fluctuations in disordered mesoscopic conductors.

Statistics of current fluctuations in mesoscopic coherent conductors at nonzero frequencies

We formulate a general approach which describes statistics of current fluctuations in mesoscopic coherent conductors at arbitrary frequencies and in the presence of interactions. Applying this approach to the non-interacting case, we analyze frequency dispersion of the third cumulant of the current operator

Josephson current in ballistic heterostructures with spin-active interfaces

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Current fluctuations and electron-electron interactions in coherent conductors

at frequencies well below both the inverse charge relaxation time and the inverse electron dwell time. This dispersion turns out to be important in the frequency range comparable to applied voltages. For comparatively transparent conductors it may lead to the sign change of

Andreev interferometer with three superconducting electrodes

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Proximity-induced screening and its magnetic breakdown in mesoscopic hybrid structures

We develop a general microscopic theory of dc Josephson effect in hybrid superconductor\char21{}normal-metal\char21{}superconductor structures with ballistic electrodes and spin-active normal-metal\char21{}superconductor (NS) interfaces. We establish a direct relation between the spectrum of Andreev levels and the Josephson current which contains complete information about nontrivial 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

Current-biased Andreev interferometer

\ensuremath{\pi}

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

-junction state in the systems under consideration. We also analyze resonant enhancement of the supercurrent in gate-voltage-driven nanojunctions. As compared to the nonmagnetic case, this effect can be strongly modified by spin-dependent scattering at NS interfaces.