Magneto-optical analysis of second-peak effect in BSCCO single crystals
INFM-UdR Torino Politecnico INFN, Sezione di Torino
Dipartimento di Fisica, Politecnico di Torino
C.so Duca degli Abruzzi 24, 10129 Torino, Italy
Accepted: 27 September 2002
We report on magneto-optical (MO) analysis on slightly overdoped single crystals of +x, focusing on the second-peak effect. In particular, we measure the local values of the virgin magnetisation, M, and, for the first time in BSCCO, at our best knowledge, of the local current density, J, as a function of the local magnetic induction field, Bz. Patterns clearly due to the second-peak effect are observed and mutually compared. From the same analysis repeated in different sample zones having the same size, it turns out that the second peak slightly shifts with the position inside the sample. The peak sharpness and depth decrease when the size of the considered region increases, whereas the peak disappears if the region includes several defects observable at the MO resolution. All the experimental evidences point towards a correlation between the second-peak effect and the local disorder at different scales.
PACS: 74.25.Dw – Superconductivity phase diagrams / 74.60.Ge – Flux pinning, flux creep, and flux-line lattice dynamics / 74.72.Hs – Bi-based cuprates
© EDP Sciences, 2002