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| VOLUME 91 | ISSUE 1 |
PAGE 32
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| Pinning of spiral fluxons by giant screw dislocations in YBa2Cu3O7-δ single crystals: Josephson analog of the fishtail effect
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S. Sergeenkov+, L. Jr. Cichetto+, V. A. G. Rivera+, C. Stari+*, E. Marega , C. A. Cardoso+, F. M. Araujo-Moreira+
+Departamento de Física e Engenharia Física, Grupo de Materiais e Dispositivos, Centro Multidisciplinar para
o Desenvolvimento de Materiais Cerâmicos, Universidade Federal de S o Carlos, So Carlos, SP, 13565-905 Brazil
*Instituto de Física, Facultad de Ingenieria, Julio Herrera y Reissig 565, C.C. 30, 11000 Montevideo, Uruguay
Instituto de Física, USP, So Carlos, SP, 13560-970 Brazil
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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.
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