Where does the transport current flow in Bi2Sr2CaCu2O8 crystals?

A new measurement technique for investigation of vortex dynamics is introduced. The distribution of the transport current across a crystal is derived by a sensitive measurement of the self-induced magnetic field of the transport current. We are able to clearly mark where the flow of the transport current is characterized by bulk pinning, surface barrier, or a uniform current distribution. One of the novel results is that in BSCCO crystals most of the vortex liquid phase is affected by surface barriers resulting in a thermally activated apparent resistivity. As a result the standard transport measurements in BSCCO do not probe the dynamics of vortices in the bulk, but rather measure surface barrier properties.Comment: 11 pages, 4 figures, accepted for publication in Natur

FIRST ORDER TRANSITION OF THE VORTEX LATTICE IN DISORDERED BI-2212 CRYSTALS

Keywords: Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed

THERMODYNAMIC OBSERVATION OF FIRST-ORDER VORTEX-LATTICE MELTING TRANSITION IN BI2SR2CACU2O8

International audienceThe lattice of magnetic flux lines that can permeate a type ii superconductor, such as the high-transition-temperature copper oxide materials, melts from a solid-like stale to a liquid-like state at a temperature below the superconducting transition temperature. Contrary to the predictions of mean-field theory, this phase transition in Bi2Sr2CaCu2O8 is found to be first-order. The vortex liquid discontinuously expands on freezing

Vortex Line Fluctuations in Superconductors from Elementary Quantum Mechanics

Concepts from elementary quantum mechanics can be used to understand vortex line fluctuations in high-temperature superconductors. Flux lines are essentially classical objects, described by a string tension, their mutual repulsion, and interactions with pinning centers. The classical partition function, however, is isomorphic to the imaginary time path integral description of quantum mechanics. This observation is used to determine the thermal renormalization of critical currents, the decoupling field, the flux lattice melting temperature at low and moderate inductions, and to estimate the degree of entanglement in dense flux liquids. The consequences of the ``polymer glass'' freezing scenario, which assumes that the kinetic constraints of entanglement prevent field cooled flux liquids from crystallizing, are reviewed.Comment: 24 pages, plain TeX, Report # CMT-HU-N0