Reversing non-local transport through a superconductor by electromagnetic excitations

Superconductors connected to normal metallic electrodes at the nanoscale provide a potential source of non-locally entangled electron pairs. Such states would arise from Cooper pairs splitting into two electrons with opposite spins tunnelling into different leads. In an actual system the detection of these processes is hindered by the elastic transmission of individual electrons between the leads, yielding an opposite contribution to the non-local conductance. Here we show that electromagnetic excitations on the superconductor can play an important role in altering the balance between these two processes, leading to a dominance of one upon the other depending on the spatial symmetry of these excitations. These findings allow to understand some intriguing recent experimental results and open the possibility to control non-local transport through a superconductor by an appropriate design of the experimental geometry.Comment: 6 pages, 3 figure

Reconfigurable superconducting vortex pinning potential for magnetic disks in hybrid structures

High resolution scanning Hall probe microscopy has been used to directly visualise the superconducting vortex behavior in hybrid structures consisting of a square array of micrometer-sized Py ferromagnetic disks covered by a superconducting Nb thin film. At remanence the disks exist in almost fully flux-closed magnetic vortex states, but the observed cloverleaf-like stray fields indicate the presence of weak in-plane anisotropy. Micromagnetic simulations suggest that the most likely origin is an unintentional shape anisotropy. We have studied the pinning of added free superconducting vortices as a function of the magnetisation state of the disks, and identified a range of different phenomena arising from competing energy contributions. We have also observed clear differences in the pinning landscape when the superconductor and the ferromagnet are electron ically coupled or insulated by a thin dielectric layer, with an indication of non-trivial vortex-vortex interactions. We demonstrate a complete reconfiguration of the vortex pinning potential when the magnetisation of the disks evolves from the vortex-like state to an onion-like one under an in-plane magnetic field. Our results are in good qualitative agreement with theoretical predictions and could form the basis of novel superconducting devices based on reconfigurable vortex pinning sites

Dependence of penetration depth, microwave surface resistance and energy gap of MgB(2) thin films on their normal-state resistivity

Jin BB, Dahm T, Iniotakis C, et al. Dependence of penetration depth, microwave surface resistance and energy gap of MgB(2) thin films on their normal-state resistivity. Superconductor Science and Technology. 2005;18(1):L1-L4.The dependences of magnetic field penetration depth at zero temperature lambda(0), microwave surface resistance R(s) and pi -band energy gap at zero temperature Delta(pi)(0) on the normal-state resistivity fight above the critical, rho(0), were studied for MgB(2) thin films prepared by different temperature. techniques by employing a sapphire resonator technique. We found that the zero-temperature penetration depth lambda(0) data could be well fitted by lambda(L)(1 + xi(0)/l)(1/2) yielding a London penetration depth lambda(L) of 34.5 nm, where xi(0) is the coherence length, and l is the mean free path determined from rho(0). The surface resistance R(s) at 15 and 20 K increases roughly linearly with rho(0). The observed increase of Delta(pi)(0) with rho(0) and the decrease of T(c) indicate the expected effects of interband impurity scattering within an extended BCS approach. The low values of R(s) and lambda(0) in conjunction with the large coherence length for epitaxial films are potentially attractive for applications in electronics and microwave technology