Münster 1999 – scientific programme

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TT: Tiefe Temperaturen

TT 24: Vortexdynamik und Pinning

TT 24.4: Invited Talk

Friday, March 26, 1999, 10:30–11:00, F2

Vortex Pinning and Critical Currents in High-Tc Superconductors: — •J.R. Thompson — Oak Ridge National Laboratory, Oak Ridge, TN 37831-6061

Many proposed applications of high-Tc superconductors require that they conduct high density currents in significant magnetic fields. This means that vortices in the material must be immobilized, since their movement dissipates energy. Vortices can be pinned by defects that locally depress the order parameter. Most effective are columnar defects that match the linear geometry and transverse length scale of a vortex. We show that correlated disorder, in the form of randomly oriented ion tracks, can greatly enhance the (nominally loss-free) current density J and reduce its decay with time in several families of HTS materials. These include Bi-2212/Ag tapes, Hg-1223 bulk ceramic and thin films, and Tl-based HTS [APL, 1996]. Irradiation with energetic (0.8 GeV) protons generates columnar defects that are visible by TEM, via induced fission of heavy nuclei, e.g., Bi, Hg, Tl, .... The fission fragments create permanent, highly splayed tracks that trap vortices efficiently. Following an overview, we analyze the effective pinning energy U(J,H) in Bi-2212. In the Hg-cuprate family, we show that increasing the superconductive anisotropy leads to a recovery of variable range vortex hopping [PRL, in press], similar to that observed in YBCO containing parallel columnar defects [PRL, 1997].

The Oak Ridge National Laboratory is managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy under contract number DE-AC05-96OR22464. Portions of this work were supported by NSF grant DMR 95-10731.