program abstracts
Saturday, 3G-05, 12:05-12:10
Vortex Diode Effect in Pinning Enhanced Thin Films
J. H. Durrell
S. A. Harrington, H. Wang*, J. L. MacManus-Driscoll
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, CAMBRIDGE, CB2 3QZ, UK.
(*) Dept. of Electrical and Computer Engineering, Texas A & M University, College Station, TX 77843
Tel +44 1223 331693, Fax +44 1223 334373, jhd25@cam.ac.uk
As an anisotropic material YBCO exhibits a distinct maximum for a critical current applied in-plane, which is often referred to as the "intrinsic pinning peak". This is due to both the layered structure, with this effect being more pronounced at lower temperatures, and to the mass anisotropy of the charge carriers the contribution of which is described by a scaling law. For in-plane fields in highly geometrically anisotropic thin films this orientation also corresponds to that of maximum surface pinning. In vicinal YBCO thin films where the in-plane and surface parallel configurations are different surface pinning has been shown to be non-negligible. We have found that in YBCO thin films with rare earth tantalate dopants added to enhance pinning the magnitude of the intrinsic peak can be strongly controlled by the direction of the Lorentz force. We find that by reversing field or current direction a variation in Ic of over 10% can be observed at 77 K and 0.25 T. We explain this observation in terms of the microstructure of the films and the effect of the microstructure on surface pinning. We observe that such a thin film is, in effect, an inverse diode where voltage is zero up to a certain current, which depends on the current direction. In a conventional diode it is current that is zero up to a certain voltage, which depends on the polarity. There is potential to exploit this technique to make coated conductors with current direction sensitive critical current properties.
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