The Two-dimensional Vibrating Reed: A Study of Anisotropic Pinning in High-temperature Superconductors

Author： Karelina Anna Braun Hans Endres Martin Rainer Dierk

ISSN： 0022-2291

Source： Journal of Low Temperature Physics, Vol.146, Iss.5-6, 2007-03, pp. : 681-695

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Abstract

The pinning of flux lines on point-like defects in superconductors depends on both the magnitude and the symmetry of the order parameter. We study the anisotropy of pinning in untwinned single crystals of YBa₂Cu₃O and crystals of Bi₂Sr₂CaCu₂O employing a modified vibrating reed technique with two degrees of freedom. The pinning potential is calculated for an anisotropic d-wave superconductor in the approximation of a single pancake vortex interacting with a single point defect. The response of the reed to pinning potentials with two- and fourfold symmetry is modeled. The appearance of a twofold symmetry is demonstrated for YBa₂ Cu₃O crystals. The effect of the fourfold symmetric component is masked by flux creep effects in our experiments.