Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 17: Superconductivity: Properties and Electronic Structure

TT 17.2: Vortrag

Montag, 16. März 2015, 15:15–15:30, H 2053

Magnetic field dependence of the superconducting proximity effect in a two atomic layer thin metallic film — Michael Caminale, Augusto A. Leon Vanegas, Agniezka Stepniak, Hirofumi Oka, •Jeison A. Fischer, Dirk Sander, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle

The intriguing possibility to induce superconductivity in a metal, in direct contact with a superconductor, is under renewed interest for applications and for fundamental aspects [1]. The underlying phenomenon is commonly known as proximity effect. In this work we exploit the high spatial resolution of scanning tunneling spectroscopy at sub-K temperatures and in magnetic fields. We probe the differential conductance along a line from a superconducting 9 ML high Pb nanoisland into the surrounding two layer thin Pb/Ag wetting layer on a Si(111) substrate. A gap in the differential conductance indicates superconductivity of the Pb island. We observe an induced gap in the wetting layer, which decays with increasing distance from the Pb island. This proximity length is 21 nm at 0.38 K and 0 T. We find a non-trivial dependence of the proximity length on magnetic field. Surprisingly, we find that the magnetic field does not affect the induced superconductivity up to 0.3 T. However, larger fields of 0.6 T suppress superconductivity in the wetting layer, where the Pb island still remains superconducting. We discuss the unexpected robustness of induced superconductivity in view of the high electronic diffusivity in the metallic wetting layer.

[1] Guéron et al. Phys. Rev. Lett. 77, 3025 (1996);

Xiang et al. Nat. Nano. 1, 208 (2006);

Wang et al. Phys. Rev. Lett. 100, 197002 (2008).