Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 7: Superconductivity & Solids At Low Temperature - Poster Session
TT 7.59: Poster
Montag, 27. März 2006, 14:00–17:45, P1
Vortex Matching in Niobium Films with Periodic Pinning Arrays produced by Micellar Technique — •M. Oettinger1, J. Eisenmenger1, C. Steiner1, C. Pfahler1, S. Brieger1, A. Plettl1, A. Dietrich1, B. Koslowski1, H.-G. Boyen1, A. Ethirajan1, P. Walther2, and P. Ziemann1 — 1Abteilung Festkörperphysik, Universität Ulm, D-89069 Ulm, Germany — 2Zentrale Einheit Elektronenmikroskopie, Universität Ulm, D-89069 Ulm, Germany
An enhanced stability of a vortex lattice is expected whenever it matches a regular array of pinning centers without disturbing its preferred triangular order. The observation of such matching effects is challenging at temperatures much smaller than the critical temperature since artificial pinning centers should have sizes of a few nanometers, i.e. comparable to the coherence length, and should be periodically arranged. For the preparation of a triangular lattice of artificial pinning centers we first prepare a closed packed monolayer of HAuCl4 loaded inverse micelles of diblock-copolymers onto a substrate. By applying a H-plasma the micelles are transformed into a triangular lattice of Au particles with diameters ≈ 10 nm. The particles serve as an etching masks for patterning arrays of pillars into the surface of a Si substrate. In a Nb thin film grown on top, pinning centers are formed at the pillars. Clear matching effects are observed even at temperatures much lower than the critical temperatures. Moreover an unusual "second" critical current is observed, indication two very different types of pinning mechanisms: Strong pinning on artificial pinning centers and weaker pinning by natural, randomly positioned pinning centers and "caging" in interstitial regions.