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Superconducting correlations may propagate between two superconductors separated by a tiny insulating or metallic barrier, allowing a dissipation-less Josephson current to flow. In the presence of a magnetic field, the maximum supercurrent oscillates and each oscillation corresponding to the entry of one Josephson vortex into the barrier. Josephson vortices are conceptual blocks of advanced quantum devices such as coherent terahertz generators or qubits for quantum computing, in which on-demand generation and control is crucial. In our lecture we describe a series of recent experiments in which we mapped superconducting correlations in S-N junctions [1,2] as well as inside SNS proximity Josephson junctions using scanning tunneling microscopy [3].
Unexpectedly, we found that when an external magnetic field is applied, the proximity effect in N is suppressed locally, thus forming a series of “nano-holes”. These were identified as individual Josephson vortex cores in which the proximity mini-gap is suppressed and the normal state recovered. By following the Josephson vortex formation and evolution we demonstrate that they originate from quantum interference of Andreev quasiparticles, and that the phase portraits of the two superconducting quantum condensates at edges of the junction decide their generation, shape, spatial extent and arrangement [3]. On the basis of our observation we suggest a novel SNS device which may be used for generation and control of Josephson vortices by applying supercurrents through the superconducting leads of the junctions, that is, by purely electrical means without any need for a magnetic field. Such devices are easily size-scalable, a crucial step towards high-density on-chip integration of superconducting quantum devices.

[1] L. Serrier-Garcia, et al. Phys. Rev. Lett. 110, 157003 (2013)
[2] Ch. Brun et al Nature Physics 10, 444 (2014)
[3] Roditchev D., et al. Nature Physics 11, 332 (2015)

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