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VOLUME 91 | ISSUE 1 | PAGE 32
Pinning of spiral fluxons by giant screw dislocations in YBa2Cu3O7-δ single crystals: Josephson analog of the fishtail effect
Abstract
By using a highly sensitive homemade AC magnetic susceptibility technique, the magnetic flux penetration has been measured in YBa2Cu3O7-δ single crystals with giant screw dislocations (having the structure of the Archimedean spirals) exhibiting a=3 spiral turnings, the pitch b=18.7 μm and the step height c=1.2 nm (the last parameter is responsible for creation of extended weak-link structure around the giant defects). The magnetic field applied parallel to the surface enters winding around the weak-link regions of the screw in the form of the so-called spiral Josephson fluxons characterized by the temperature dependent pitch bf(T). For a given temperature, a stabilization of the fluxon structure occurs when bf(T) matches b (meaning an optimal pinning by the screw dislocations) and manifests itself as a pronounced low-field peak in the dependence of the susceptibility on magnetic field (applied normally to the surface) in the form resembling the high-field (Abrikosov) fishtail effect.