Electron Transport in Hybrid Ferromagnetic/Superconducting Nanostructures

We observe large amplitude changes in the resistance of ferromagnetic (F) wires at the onset of superconductivity of adjacent superconductors (S). New sharp peaks of large amplitude are found in the magnetoresistance of the F-wires. We discuss a new mechanism for the long-range superconducting proximity effect in F/S nanostructures based on the analysis of the topologies of actual Fermi-surfaces in ferromagnetic metals.Comment: 7 pages in LaTeX, 5 eps figures. Submitted to the Proceedings of MS200

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

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

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

Double-injector source of spin polarized current with controllable polarization

We present low-temperature measurements of Co/Al spin valves with a double-injector source of spin polarized current. Using an in-plane magnetic field, the injector electrodes were magnetized in opposite directions. The spin polarization of the injected current was controlled by changing the ratio of currents through the two electrodes and was continuously varied from zero up to the maximum spin polarization of Co. This result was verified by measuring the spin valve signal, using the detector electrode magnetized to align with one of the injectors. This source can be used for spintronic applications as well as in research on hybrid ferromagnet/superconductor structures

Long-range coherence and mesoscopic transport in N-S metallic structures

We review the mesoscopic transport in a diffusive proximity superconductor made of a normal metal (N) in metallic contact with a superconductor (S). The Andreev reflection of electrons on the N-S interface is responsible for the diffusion of electron pairs in N. Superconducting-like properties are induced in the normal metal. In particular, the conductivity of the N metal is locally enhanced by the proximity effect. A re-entrance of the metallic conductance occurs when all the energies involved (e.g. temperature and voltage) are small. The relevant characteristic energy is the Thouless energy which is $\hbar$ divided by the diffusion time for an electron travelling throughout the sample. In loop-shaped devices, a 1/T temperature-dependent oscillation of the magnetoresistance arises with a large amplitude from the long-range coherence of low-energy pairs.Comment: Review paper, 13 pages with 5 included epsf figures, to appear in Superlattices and Microstructures, minor change

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