17 research outputs found
Equilibrium First-Order Melting and Second-Order Glass Transitions of the Vortex Matter in BiSrCaCuO
The thermodynamic phase diagram of BiSrCaCuO was mapped
by measuring local \emph{equilibrium} magnetization in presence of
vortex `shaking'. Two equally sharp first-order magnetization steps are
revealed in a single temperature sweep, manifesting a liquid-solid-liquid
sequence. In addition, a second-order glass transition line is revealed by a
sharp break in the equilibrium slope. The first- and second-order lines
intersect at intermediate temperatures, suggesting the existence of four
phases: Bragg glass and vortex crystal at low fields, glass and liquid at
higher fields.Comment: 5 pages, 4 figures. To be published in Phys. Rev. Let
Interplay of Anisotropy and Disorder in the Doping-Dependent Melting and Glass Transitions of Vortices in BiSrCaCuO
We study the oxygen doping dependence of the equilibrium first-order melting
and second-order glass transitions of vortices in
BiSrCaCuO. Doping affects both anisotropy and
disorder. Anisotropy scaling is shown to collapse the melting lines only where
thermal fluctuations are dominant. Yet, in the region where disorder breaks
that scaling, the glass lines are still collapsed. A quantitative fit to
melting and replica symmetry breaking lines of a 2D Ginzburg-Landau model
further reveals that disorder amplitude weakens with doping, but to a lesser
degree than thermal fluctuations, enhancing the relative role of disorder.Comment: 4 pages, 4 figure
Evidence for a Two-stage Melting Transition of the Vortex Matter in Bi2Sr2Ca1Cu2O8+d Single Crystals obtained by Muon Spin Rotation
From muon spin rotation measurements on under- to overdoped Bi-2212 crystals
we obtain evidence for a two-stage transition of the vortex matter as a
function of temperature. The first transition is well known and related to the
irreversibility line (IL). The second one is located below the IL and has not
been previously observed. It occurs for all three sets of crystals and is
unrelated to the vortex mobility. Our data are consistent with a two-stage
melting scenario where the intra-planar melting of the vortex lattice and the
inter-planar decoupling of the vortex lines occur independently.Comment: 9 pages and 3 figure
Possible new vortex matter phases in BSCCO
The vortex matter phase diagram of BSCCO crystals is analyzed by
investigating vortex penetration through the surface barrier in the presence of
a transport current. The strength of the effective surface barrier, its
nonlinearity, and asymmetry are used to identify a possible new ordered phase
above the first-order transition. This technique also allows sensitive
determination of the depinning temperature. The solid phase below the
first-order transition is apparently subdivided into two phases by a vertical
line extending from the multicritical point.Comment: 11 pages, 3 figures, accepted for publication in PR
Electron irradiation effect on the double hump magnetization loop in BSCOO crystals
communication a : International Conference on Materials and Mechanisms of Superconductivity, High Temperature, Kanazawa (JP), 22-26 July 1991SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1297 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Elaboration, microstructure, propriétés électriques et magnétiques de matériaux textures dans les systèmes Nd-Ce-Cu-O et Bi-Sr-Ca-Cu-O
Superconducting textured materials were grown from the melt by a floating zone technique in the Nd-Ce-Cu-O and Bi-Sr-Ca-Cu-O systems. The influence of growth conditions and starting compositions on the microstructures and phase composition of the samples were studied by optical microscopy under polarized light, electron microprobe analysis and X-ray diffraction. The superconducting properties of these samples were examined by both electrical resistivity and magnetic measurements. A very strong influence of the microstructure on the superconducting properties as well as a magnetic and electrical anisotropy were shown. In the case of the Bi-Sr-Ca-Cu-O system, critical current densities ranging from 1 600 to 3 000 A.cm were measured at 77 K.Des matériaux supraconducteurs texturés ont été élaborés à partir de l'état liquide dans les systèmes Nd-Ce-Cu-O et Bi-Sr-Ca-Cu-O par une technique de fusion de zone. L'influence des conditions de croissance et des compositions initiales sur la microstructure des échantillons a été étudiée par microscopie optique en lumière polarisée, microsonde électronique et diffraction des rayons X. Les propriétés supraconductrices des échantillons ont été examinées par des mesures électriques et magnétiques. Il a été observé une forte influence de la microstructure sur les propriétés supraconductrices ainsi qu'une anisotropie électrique et magnétique. Dans le cas du système Bi-Sr-Ca-Cu-O, les densités de courant critique mesurées à 77 K sont comprises entre 1 600 et 3 000 A.cm