H. Pastoriza

Imaging the structure of the interface between symmetries interconnected by a discontinuous transition

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 a 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.

Effects of reduced dimensionality on the energy dissipation of superconducting Bi2Sr2CaCu2O8 compounds

Abstract Strong experimental evidence of the important role of the reduced dimensionality of the vortices in the c direction in BSCCO (2 2 1 2) crystals is provided. As a result of this, it is shown that the long-range order of the vortex in the c direction is destroyed by the disorder induced by thermal fluctuations as well as by the nonuniform distribution of the pancake vortices in low-temperature ZFC experiments.

Direct determination of the collective pinning radius in the cuprate superconductor Bi2Sr2CaCu2O8+δ

We study the onset of the irreversible magnetic behavior of vortex matter in micron-sized

Meissner fraction in insulating samples of oxide superconductors

{\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}

Geometrical Confinement Effects in Layered Mesoscopic Vortex Matter

single crystals by using silicon micro-oscillators. We find an irreversibility line appearing well below the thermodynamic Bragg-glass melting line at a magnetic field which increases both with increasing the sample radius and with decreasing the temperature, paradoxically implying the existence of a reversible vortex solid. We show that at this irreversibility line, the sample radius can be identified with the crossover length between the Larkin and the random-manifold regimes of the vortex-lattice transverse roughness. Our method thus allows to determine, as a function of temperature and applied magnetic field, the minimum size of a vortex system that can be collectively pinned, or the so-called three-dimensional weak collective pinning Larkin radius, in a direct way.

Consequences of 3D-2D vortex decoupling on the phase diagram of HTS

Abstract The tendency towards superconducting granularity with sample degradation is a common feature of oxide superconductors. We present magnetic, transport and calorimetic results in LiTi 2 O 4 which show that the topological tendency to segregate the superconducting state into islands surrounded by thin insulating layers is related to the structure of the material rather than to a mechanism associated to high T c . We emphasize that insulating samples with small Meissner fraction can have a superconducting volume fraction close to unity.

Phase diagram of the mixed state of Bi2Sr2CaCu2O8 single crystals: first order phase transition at the irreversibility line

We study the geometrical confinement effect in Bi

Vortex matter freezing inBi2Sr2CaCu2O8samples with a very dense distribution of columnar defects

_{2}