UNSPECIFIED. (2002) Modelling the effective potential for persistent currents in annular discs of YBCO with coherent Josephson nanostructures. PHYSICS LETTERS A, 299 (5-6). pp. 607-615. ISSN 0375-9601

Abstract

Darhmaoui and Jung (Phys. Rev. B 57 (1998) 8009) recently reported measurements of persistent current dissipation in the a-b plane of YBCO thin films. Their results conformed with the Ambegaokar-Baratoff empirical formulation for the energy barrier as a function or the critical current density, J(c), given by U-eff(J) = J(c)(T)[a(1) exp(-3pi/2 J/J(c0)) + a(2) exp (-9pi/2 J/J(c0))]. where J(c0) is the value of J(c) at 0 K. In this Letter we provide a qualitative theoretical model explaining the emergence of exponentials in the above formula and their arguments. The model is based on a picture of the vortex lattice as a series of rings of vortices around the annuli used. For small magnetic fields we show how the vortex-vortex interaction varies exponentially with field. We utilise an XY model and to incorporate the geometry of the annular specimens we assume vortices are coupled within each concentric ring but neighbouring rings are effectively uncoupled. This latter assumption, with a second which assumes magnetic terms are much larger than inter-vortex coupling, enables us to incorporate the variation in magnetic field across the annuli and hence determine the factors 3pi/2 and 9pi/2 in U-eff(J). We obtain very good agreement with both exponentials in U-eff (J). (C) 2002 Elsevier Science B.V. All rights reserved.

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