Interfacial Tension and Interface Delocalization Phase Boundary for Strongly Type-I Superconductors

We analytically determine the interface delocalization (or wetting) transition phase boundary in the limit of strongly type-I superconductors. In particular, within Ginzburg–Landau theory we derive an analytic expression for the reduced surface tension, _SC/N, of a type-I superconductor. We find that the truncated expansion (where is the Ginzburg–Landau parameter) is so accurate in the entire type-I regime that derivation of higher-order terms is unnecessary. We further derive an expression for the wall/superconductor interfacial tension which again proves accurate across a broad range of values. These expansions allow us to locate the low- interface delocalization phase boundary accurately, complementing previous numerical results for the wetting phase diagram.     

The frozen-field approximation and the Ginzburg-Landau equations of superconductivity

The Ginzburg-Landau (GL) equations of superconductivity provide a computational model for the study of magnetic flux vortices in type-II superconductors. In this article it is shown through numerical examples and rigorous mathematical analysis that the GL model reduces to the frozen-field model when the charge of the Cooper pairs (the superconducting charge carriers) goes to zero while the applied field stays near the upper critical field.     

Oblique Vortex Lattice Implies Unconventional Pairing Symmetry in High Temperature Superconductors

The symmetry of order parameters of YBa₂Cu₃O_{7 –} high temperature superconductor was studied with the Ginzburg–Landau theory. The vortex lattice of a YBa₂Cu₃O₇ superconductor is oblique at a temperature well below the transition temperature T _c, where the mixed s– state is expected to have the lowest energy, whereas very close to T _c, the -wave is slightly lower in energy, and a triangular vortex lattice recovers. The coexistence and the coupling between the s- and d-waves would account for the unusual behaviors such as the upward curvature of the upper critical field curve H _C2(T).     

Superconductivity from Repulsion: Ginzburg–Landau Phenomenology of Cuprates

We develop Ginzburg–Landau approach to the problem of superconducting pairing with large momentum under screened Coulomb repulsion (η_K-pairing). Two-component order parameter arising in this scheme can be associated with charge and orbital current degrees of freedom of the relative motion of η_K-pair corresponding to superconducting and orbital antiferromagnetic ordered states, respectively. All basic features of the phase diagram of cuprate superconductors result directly from the η_K-pairing concept. PACS numbers: 74.20.-z, 74.20.De, 74.72.-h.     

Evolution of Two-Band Superfluidity from Weak to Strong Coupling

We analyze the evolution of two-band superfluidity from the weak to the strong coupling (Bardeen–Cooper–Schrieffer to Bose–Einstein condensation) limit. We find that population imbalances between the two bands can be created by tuning the intraband or interband (Josephson) interactions. In addition, when the Josephson interband interaction is tuned from negative to positive values, a quantum phase transition occurs from a 0-phase to a π-phase state, depending on the relative phase of the two order parameters. We also find two undamped low energy collective excitations corresponding to in-phase phonon (Goldstone) and out-of-phase exciton (finite frequency) modes. Lastly, we derive the coupled Ginzburg–Landau equations, and show that they reduce to coupled Gross–Pitaevskii equations for two types of weakly interacting bosons (tightly bound fermions) in the BEC limit.      

Wetting Phenomena in bcc Binary Alloys

We study the influence of the surface orientation on the wetting behavior of bcc binary alloys, using a semiinfinite lattice model equivalent to a nearest-neighbor Ising antiferromagnet in an external magnetic field. This model describes alloys that exhibit a continuous B2–A2 order–disorder transition, such as FeAl or FeCo. For symmetry-breaking surfaces like (100), an effective ordering surface field g ₁0 emerges. Such a field not only crucially affects the surface critical behavior at bulk criticality, but also gives rise to wetting transitions below the critical temperature T _c. Starting from the mean-field theory for the lattice model and making a continuum approximation, a suitable Ginzburg–Landau model is derived. Explicit results for the dependence of its parameters (e.g., of g ₁) on the microscopic interaction constants are obtained. Utilizing these in conjunction with Landau theory, the wetting phase diagram is calculated.     

On the Electron–Electron Interaction in Superconductors

By using an attractive potential that varies in reverse proportion with respect to the third power of the distance between the two particles, we resolved the Schrodinger equation for an electron pair. We applied these statements to superconductors and obtained a good agreement with experimental data and BCS theory.     

Non‐weak/strong solutions in gas dynamics: a C11 p‐version STLSFEF in Eulerian frame of reference using ρ, u,p primitive variables

This paper presents a space–time least squares finite element formulation of one‐dimensional transient Navier–Stokes equations (governing differential equations: GDE) for compressible flow in Eulerian frame of reference using ρ, u, p as primitive variables with C¹¹ type p‐version hierarchical interpolations in space and time. Time marching procedure is utilized to compute time evolutions for all values of time. For high speed gas dynamics the C¹¹ type interpolations in space and time possess the same orders of continuity in space and time as the GDE. It is demonstrated that with this approach accurate numerical solutions of Navier–Stokes equations are possible without any assumptions or approximations. In the approach presented here SUPG, SUPG/DC, SUPG/DC/LS operators are neither used nor needed. Time accurate numerical simulations show resolution of shock structure (i.e. shock speed, shock relations and shock width) to be in excellent agreement with the analytical solutions. The role of diffusion i.e. viscosity (physical or artificial) and thermal conductivity on shock structure is demonstrated. Riemann shock tube is used as a model problem. True time evolutions are reported beginning with the first time step until steady shock conditions are achieved. In this approach, when the computed error functionals become zero (computationally), the computed non‐weak solutions have characteristics as those of the strong solutions of the gas dynamics equations. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of Superconducting 2212 Phase in the Bi–Pb–Sr–La–Cu–O System

There have been no report about synthesis of the Bi-2212 compound in the Bi–r–La–Cu–O system. We have succeeded in synthesizing the Bi-2212 compound by partial substitution of Pb for Sr and/or Bi in the Bi–Sr–La–Cu–O system. Two samples of nearly the single 2212 phase have been obtained at a nominal composition of Bi_1.5Pb_0.5Sr_2.5La_0.5Cu₂O _z . Both of the samples crystallize in a psedotetragonal lattice, and their lattice parameters are a = 0.5476 nm and c = 3.085 nm or a = 0.5479 nm and c = 3.055 nm. They are both superconductors. The sample with longer lattice parameter c shows an onset of the resistivity drop and zero resistivity at higher temperatures of about 40 K and about 13 K, respectively. This sample also shows a diamagnetic signal starting at about 35 K with lowering temperature.