Non-local Transport in Superconductor–Ferromagnet Hybrid Structures

DOI: 10.1007/978-3-642-20158-5_4

ABSTRACT We review recent experimental results on non-local transport in superconductor–ferromagnet hybrid structures. We will focus
mainly on crossed Andreev reflection and its relation to competing non-local transport phenomena such as elastic cotunneling,
charge imbalance and spin diffusion.

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    ABSTRACT: We consider transport in a three-terminal device attached to one superconducting and two normal-metal terminals, using the circuit theory of mesoscopic superconductivity. We compute the nonlocal conductance of the current out of the first normal-metal terminal in response to a bias voltage between the second normal-metal terminal and the superconducting terminal. The nonlocal conductance is given by competing contributions from crossed Andreev reflection and electron cotunneling, and we determine the contribution from each process. The nonlocal conductance vanishes when there is no resistance between the superconducting terminal and the device, in agreement with previous theoretical work. Electron cotunneling dominates when there is a finite resistance between the device and the superconducting reservoir. Dephasing is taken into account, and the characteristic time scale is the particle dwell time. This gives rise to an effective Thouless energy. Both the conductance due to crossed Andreev reflection and electron cotunneling depend strongly on the Thouless energy. We suggest experimental determination of the conductance due to crossed Andreev reflection and electron cotunneling in measurement of both energy and charge flow into one normal-metal terminal in response to a bias voltage between the other normal-metal terminal and the superconductor.
    Physical Review B 12/2006; 74(21). DOI:10.1103/PhysRevB.74.214510 · 3.66 Impact Factor
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    ABSTRACT: We examine here electronic transport in nanoscale systems where normal and ferromagnetic probes are attached to a conventional superconductor. While reviewing the long-studied effects of Andreev reflection and charge imbalance, we concentrate on two recently predicted coherent, nonlocal processes known as crossed Andreev reflection and elastic co-tunnelling. These processes can occur when two spatially separated normal or ferromagnetic probes are separated by a distance comparable to the coherence length of the superconductor. Here we show that normal probes, by avoiding some of the experimental and theoretical complications of ferromagnetic probes, may offer a better opportunity to examine these processes.
    New Journal of Physics 05/2007; 9(116):1367-263036895. DOI:10.1088/1367-2630/9/5/116 · 3.67 Impact Factor
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    ABSTRACT: We consider a hybrid system consisting of two normal metal leads weakly connected to a superconductor. Current-current correlations of the normal leads are studied in the tunneling limit at subgap voltages and temperatures. We find that only two processes contribute to the cross-correlation: the crossed Andreev reflection (emission of electrons in different leads) and the elastic cotunneling. Both processes are possible due to the finite size of the Cooper pair. Noise measurements can thus be used to probe directly the superconducting wave function without the drawbacks appearing in average current measurements where the current is dominated by direct Andreev reflection processes. By tuning the voltages it is possible to change the sign of the cross correlation. Quantitative predictions are presented both in the diffusive and ballistic regimes.
    EPL (Europhysics Letters) 11/2003; 67(1). DOI:10.1209/epl/i2003-10293-9 · 2.27 Impact Factor