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We have investigated the response of 3D Bi 2 Sr 2 CaCu 2 O 8 vortex structures to a weak perturbation induced by 2D Fe pinning structures acting on one extremity of vortex lines. The pinning patterns were nano-engineered at the sample surface by means of either a Bitter decoration of the vortex lattice or electron-beam lithography. The commensurability conditions between 2D rigid pinning potentials and 3D elastic structures with short-range positional and long-range orientational correlation have been experimentally determined. When the 2D potential is a replica of the nonperiodic vortex structure an amplification of its interaction with the vortex structure takes place. This effect is detected only for the first matching field, becoming negligible for other matching fields. On the other hand, a periodic 2D perturbation is shown to transform the nonperiodic Bragg glass-like structure into an Abrikosov crystal with an effective Debye–Waller factor.

We make a comparative analysis of the response of the three-dimensional vortex lattice in Bi-2 Sr-2 CaCu2O8 and NbSe2 to the presence of square arrays of pinning sites localized at one extremity of the vortex crystals. The absence of the hexagonal to square symmetry transformation and the induction of a distorted hexagonal symmetry in the vortex lattice of NbSe2 contrast to the observed symmetry change in Bi2Sr2CaCu2O8. The dissimilar response in both cases is explained taking into account the vortex structure solidification mechanisms in both materials: The plastic response in the case of the layered material Bi2Sr2CaCu2O8 is suggested to be a result of the simultaneity of solidification and coupling of bidimensional pancake vortices whereas a viscous solidification is the responsible for the three-dimensional elastic response in NbSe2.

We have been able to observe with single particle resolution the interface between two structural symmetries that cannot be interconnected by a continuous transition. By means of an engineered 2D potential that pins the extremity of vortex strings an square symmetry was imposed at the surface of a 3D vortex solid. Using the Bitter decoration technique and on account of the continuous vortex symmetry we visualize how the induced structure transforms along the vortex direction before changing into the expected hexagonal structure at a finite distance from the surface., 10 pages, 5 figures

We report on symmetry changes of the bulk hexagonal vortex lattice induced by commensurate and incommensurate engineered 2D square pinning structures of Fe dots, deposited on one surface of Bi2Sr2CaCu2O8 single crystals. (C) 2004 Elsevier B.V. All rights reserved.