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TT: Tiefe Temperaturen

TT 33: Superconductivity: Vortex Dynamics, Vortex Phases, Pinning

TT 33.8: Vortrag

Freitag, 31. März 2006, 12:00–12:15, HSZ 304

Microscopic Study of Pinning Mechanisms in YBCO HTSC Films — •Tetyana Shapoval, Volker Neu, Ulrike Wolff, Ruben Hühne, Jens Hänisch, Bernhard Holzapfel, and Ludwig Schultz — IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, D-01171 Dresden, Germany

The direct microscopic imaging of flux lines is a powerful tool for the understanding of vortex pinning mechanism at natural and artificial defects and can help to increase the critical current density. For these investigations a low-temperature scanning probe microscope (Omicron Cryogenic SFM) is used, which allows AFM, MFM and STM/STS measurements in UHV combined with magnetic fields of 7 T (vertical) and 3 T (transversal) at low temperatures (9 K - 300 K). Flux lines of an YBCO film have been successfully imaged by measuring their stray field in MFM modus. The 300 nm thick film with mean roughness less than 10 nm has been prepared by off-axis PLD and has been cooled down in the microscope to 7.7 K in a magnetic field of 3 mT prior to imaging. The number of vortices that we observed corresponds to the theoretically expected one. Whereas a constant current leads to the unacceptable heating of the sample, the use of current pulses allows transport measurements, avoiding thermal movement of vortices. The depinning mechanism is studied on a structured YBCO film by in situ imaging of flux lines under the influence of increasingly larger current pulses.