Random Scattering Matrices and the Circuit Theory of Andreev Conductances

The conductance of a normal-metal mesoscopic system in proximity to superconducting electrode(s) is calculated. The normal-metal part may have a general geometry, and is described as a ``circuit'' with ``leads'' and ``junctions''. The junctions are each ascribed a scattering matrix which is averaged over the circular orthogonal ensemble, using recently-developed techniques. The results for the electrical conductance reproduce and extend Nazarov's circuit theory, thus bridging between the scattering and the bulk approaches. The method is also applied to the heat conductance.Comment: 12 pages, RevTeX, including 2 figures with eps

Andreev Probe of Persistent Current States in Superconducting Quantum Circuits

Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give continuous read-out of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.Comment: Changes made in light of referees comments; to appear in PR

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

Nonlinear Resonance of Superconductor/Normal Metal Structures to Microwaves

We study the variation of the differential conductance $G=dj/dV$ of a normal metal wire in a Superconductor/Normal metal heterostructure with a cross geometry under external microwave radiation applied to the superconducting parts. Our theoretical treatment is based on the quasiclassical Green's functions technique in the diffusive limit. Two limiting cases are considered: first, the limit of a weak proximity effect and low microwave frequency, second, the limit of a short dimension (short normal wire) and small irradiation amplitude.Comment: 11 pages, 10 figure

Enhanced superconducting proximity effect in clean ferromagnetic domain structures

We investigate the superconducting proximity effect in a clean magnetic structure consisting of two ferromagnetic layered domains with antiparallel magnetizations in contact with a superconductor. Within the quasiclassical Green's function approach we find that the penetration of the superconducting correlations into the magnetic domains can be enhanced as compared to the corresponding single domain structure. This enhancement depends on an effective exchange field which is determined by the thicknesses and the exchange fields of the two domains. The pair amplitude function oscillates spatially inside each domain with a period inversely proportional to the local exchange field. While the oscillations have a decreasing amplitude with distance inside the domain which is attached to the superconductor, they are enhancing in the other domain and can reach the corresponding normal metal value for a zero effective exchange field. We also find that the corresponding oscillations in the Fermi level proximity density of states as a function of the second domain's thickness has an growing amplitude over a range which depends on the effective exchange field. Our findings can be explained as the result of cancellation of the exchange fields induced phases gained by an electron inside the two domains with antiparallel magnetizations.Comment: 7 pages, 4 figure

Geometric phases and Andreev reflection in hybrid rings

We study the Andreev reflection of a hybrid mesoscopic ring in the presence of a crown-like magnetic texture. By calculating the linear-response conductance as a function of the Zeeman splitting and the magnetic flux through the ring, we are able to identify signatures of the Berry phase acquired by the electrons during transport. This is proposed as a novel detection scheme of the spin-related Berry phase, having the advantage of a larger signal contrast and robustness against ensemble averaging.Comment: 6 pages, 6 figures. To appear in Phys. Rev.

Coherent Electron Transport in Superconducting-Normal Metallic Films

We study the transport properties of a quasi-two-dimensional diffusive normal metal film attached to a superconductor. We demonstrate that the properties of such films can essentially differ from those of quasi-one-dimensional systems: in the presence of the proximity induced superconductivity in a sufficiently wide film its conductance may not only increase but also decrease with temperature. We develop a quantitative theory and discuss the physical nature of this effect. Our theory provides a natural explanation for recent experimental findings referred to as the ``anomalous proximity effect''.Comment: 4 Pages RevTex, 4 Postscript figures; submitted to Phys. Rev. Let

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