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Transport in hybrid systems with superconductors

We have calculated the finite-frequency current noise of a superconductor-ferromagnet quantum point contact (QPC), and we have found that measuring this noise could give access to the spin dependence of interfacial phase shifts acquired by electrons upon reflection on the QPC.

More recently, we have demonstrated the existence of higher order Andreev reflection processes when three superconducting wires are connected on a spatial region whose size is comparable to the superconducting coherence length. In particular, we have shown that a composite system of two Cooper pairs originating from one superconductor can be scattered in two correlated Cooper pairs on the other
two superconductors. This opens the way for the investigation of many new effects on both ac and dc transport in such systems, which is the subject of the new ANR contract Nanoquartets in which B. Dou-cot is participating.
In relation with "spintronic" experiments (Grenoble, Orsay) the transport properties of a superconducting junction with a precessing spin were studied. The dynamics of the magnetic impurity brings the quantum system out-of-equilibrium. Using the Keldysh technique, the model (in the dc case) has been solved exactly both analytically and numerically. Among the most remarkable results found : unusual
(with respect to the non-magnetic case) current (spin and charge) phase relations. The back-action of the spin-current on the impurity has been found to be weak deep in the superconducting phase providing a self-consistent check for the validity of the current-phase relations.