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TT: Tiefe Temperaturen

TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...

TT 18.13: Vortrag

Dienstag, 28. März 2006, 18:15–18:30, HSZ 02

Direct observation of non-local effects in superconductors — •Elvezio Morenzoni¹, Andreas Suter¹, Eugenie Kirk¹, Hubertus Luetkens^1,2, Thomas Prokscha¹, Rustem Khasanov^1,3, Michael Horisberger¹, and Nadir Garifianov⁴ — ¹Paul Scherrer Institut, CH-5232 Villigen PSI — ²TU Braunschweig, 38106 Braunschweig — ³University of Zurich, CH-8057 Zurich — ⁴Kazan Physical-Technical Institute, 420029 Kazan, Russian Federation

Applying a small magnetic field parallel to the surface of a superconductor results in the expulsion of the magnetic flux from its interior, except for a small region on the nm scale close to its surface where the local field B(z) (z depth from the surface) is heavily damped. It is very difficult to measure B(z) directly, since it extends only over a few tens of nanometer away from the surface into the material. This requires experimental probes that allow to measure the properties of such regions directly. We used the newly developed low energy muon spin rotation technique at PSI to first microscopically measure B(z) in conventional superconductors (Pb, Ta, Nb). Our measurements show that B(z) clearly deviates from an exponential decay underneath the surface and are a direct, model-independent proof for a non-local response in a superconductor. While B(z) for Nb and Pb is well described within the Pippard and BCS models, for Ta this is true to a lesser degree. We attribute this discrepancy to the fact that the superfluid density is decreased by approaching the surface on a length scale ξ₀ an effect which is not taken self-consistently into account in the mentioned models. From the quantitative analysis London penetration and coherence length are obtained.