Mean-field theory of a quasi-one-dimensional superconductor in a high magnetic field

At high magnetic field, the semiclassical approximation which underlies the Ginzburg-Landau (GL) theory of the mixed state of type II superconductors breaks down. In a quasi-1D superconductor (weakly coupled chains system) with an {\it open Fermi surface}, a high magnetic field stabilizes a cascade of superconducting phases which ends in a strong reentrance of the superconducting phase. The superconducting state evolves from a triangular Abrikosov vortex lattice in the semiclassical regime towards a Josephson vortex lattice in the reentrant phase. We study the properties of these superconducting phases from a microscopic model in the mean-field approximation. The critical temperature is calculated in the quantum limit approximation (QLA) where only Cooper logarithmic singularities are retained while less divergent terms are ignored. The effects of Pauli pair breaking (PPB) and impurity scattering are taken into account. The Gor'kov equations are solved in the same approximation but ignoring the PPB effect. We derive the GL expansion of the free energy. We obtain the specific heat jump at the transition, the sign of the magnetization and the quasi-particle excitation spectrum. The calculation is extended beyond the QLA taking into account all the pairing channels and the validity of the QLA is discussed in detail.Comment: 35 pages, RevTex, 18 figures available upon reques

Quasi-one-dimensional superconductors: from weak to strong magnetic field

We discuss the possible existence of a superconducting phase at high magnetic field in organic quasi-one-dimensional conductors. We consider in particular (i) the formation of a Larkin-Ovchinnikov-Fulde-Ferrell state, (ii) the role of a temperature-induced dimensional crossover occuring when the transverse coherence length $\xi_z(T)$ becomes of the order of the lattice spacing, and (iii) the effect of a magnetic-field-induced dimensional crossover resulting from the localization of the wave functions at high magnetic field. In the case of singlet spin pairing, only the combination of (i) and (iii) yields a picture consistent with recent experiments in the Bechgaard salts showing the existence of a high-field superconducting phase. We point out that the vortex lattice is expected to exhibit unusual characteristics at high magnetic field.Comment: To be published in Journal of Superconductivity, Proceedings of the Workshop on "Exactly Aligned Magnetic Field Effects in Low-Dimensional Superconductors" (Kyoto, Nov. 1998

Metal-insulator transition in highly conducting oriented polymers

We suggest that highly conducting oriented polymers with a fibril structure can be modeled by a regular lattice of disordered metallic wires with a random first-neighbor interwire coupling which mimics the cross-links between fibrils. We show that such a model can be described by a non-linear sigma model. Within a one-loop self-consistent approximation, we determine the position of the metal-insulator transition as a function of interwire cross-links concentration, interwire coupling and number of polymer chains in a wire.Comment: 9 pages (RevTex) + 3 postcript figure

Thermodynamics and Excitation Spectrum of a Quasi-One-Dimensional Superconductor in a High Magnetic Field

At high magnetic field, the semiclassical approximation which underlies the Ginzburg-Landau theory of the mixed state of type II superconductors breaks down. In a quasi-1D superconductor with an {\it open Fermi surface}, a high magnetic field stabilizes a cascade of superconducting phases which ends in a strong reentrance of the superconducting phase. From a microscopic mean-field model, we determine the thermodynamics and the excitation spectrum of these quantum superconducting phases.Comment: 4 pages (twocolumn) + 3 figures (upon request), RevTex, ORSAY-LPS-0

Targeted searches for gravitational waves from radio pulsars

An overview of the searches for gravitational waves from radio pulsars with LIGO and GEO is given. We give a brief description of the algorithm used in these targeted searches and provide end-to-end validation of the technique through hardware injections. We report on some aspects of the recent S3/S4 LIGO and GEO search for signals from several pulsars. The gaussianity of narrow frequency bands of S3/S4 LIGO data, where pulsar signals are expected, is assessed with Kolmogorov-Smirnov tests. Preliminary results from the S3 run with a network of four detectors are given for pulsar J1939+2134

Antiferromagnetism and single-particle properties in the two-dimensional half-filled Hubbard model: Slater vs Mott-Heisenberg

We study antiferromagnetism and single-particle properties in the two-dimensional half-filled Hubbard model at low temperature. Collective spin fluctuations are governed by a non-linear sigma model that we derive from the Hubbard model for any value of the Coulomb repulsion. As the Coulomb repulsion increases, the ground state progressively evolves from a Slater to a Mott-Heisenberg antiferromagnet. At finite temperature, we find a metal-insulator transition between a pseudogap phase at weak coupling and a Mott-Hubbard insulator at strong coupling.Comment: Revised version, to appear in EuroPhys. Letters (epl style included

Trends in Smart City Development

This report examines the meanings and practices associated with the term 'smart cities.' Smart city initiatives involve three components: information and communication technologies (ICTs) that generate and aggregate data; analytical tools which convert that data into usable information; and organizational structures that encourage collaboration, innovation, and the application of that information to solve public problems