[en] We study the U(1)XU(1) gauge field theory and suggest a new mechanism called soliton pairing to realize the microphysical phenomenon of high-T_c superconductivity. Cu-O hybridization strongly binds a added hole on each square of oxygen atoms, forming a local singlet which consists of spatially extended string of Cu⁺-O^- pairs, having a structure of quantized vortices which posses interesting dynamics. We investigate the dynamics of their phase using the variational method and obtain a superconducting soliton solution. We show that the mechanism of superconducting is understood in terms of a coupling between vortice field and string field. We discuss the relevance of the results to the high-T_c superconductivity. The theory may be useful for phenomenological calculations. We also briefly discuss the important experimental implications

[en] Although assuming that a mechanism for superconductivity is the intralayer coupling due to soliton pairing, it is demonstrated that the interlayer coupling can increase T_c. The intralayer soliton pair is augmented by interlayer scattering due to interlayer coupling. High-T_c superconductivity arises from the cooperation of the two couplings. Explicit expressions and results for the dependence of T_c of multilayer compounds on the number of Cu-O sublayers are obtained. The calculated values both for three- and four-layer Tl-base compounds and for three-layer Bi-base compounds are in agreement well with the observed T_c's respectively. This picture suggests where the room temperature superconductors will be found. The possible implications to other high-T_c superconductors (La-Ba-Cu-O and Y-Ba-Cu-O) are also discussed

[en] Using the density matrix renormalization group technique, we calculate numerically the low energy excitation spectrum and magnetization curve of the spin-1 antiferromagnetic chain in a staggered magnetic field, which is expected to describe the physics of R₂BaNiO₅(R ≠ Y) family below the Neel temperature of the magnetic rare-earth (R) sublattice. These results are valid in the entire range of the staggered field, and agree with those given by the non-linear σ model study for small fields, but differ from the latter for large fields. They are consistent with the available experimental data. The correlation functions for this model are also calculated. The transverse correlations display the anticipated exponential decay with shorter correlation length, while the longitudinal correlations show explicitly the induced staggered magnetization. (author)

[en] This paper proposes an impurity solver for the dynamical mean field theory (DMFT) study of the Mott insulators, which is based on the second order perturbation of the hybridization function. After careful benchmarking with quantum Monte Carlo results on the anti-ferromagnetic phase of the Hubbard model, it concludes that this impurity solver can capture the main physical features in the strong coupling regime and can be a very useful tool for the LDA (local density approximation) + DMFT studies of the Mott insulators with long range order. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

[en] We propose a real-space Gutzwiller variational approach and apply it to a system of repulsively interacting ultracold fermions with spin-½ trapped in an optical lattice with a harmonic confinement. Using the real-space Gutzwiller variational approach, we find that in a system with balanced spin-mixtures on a square lattice, antiferromagnetism either appears in a checkerboard pattern or forms a ring, and the antiferromagnetic order is stable in the regions where the particle density is close to one, which is consistent with the recent results obtained by the real-space dynamical mean-field theory approach. We also investigate the imbalanced case and find that the antiferromagnetic order is suppressed there. (atomic and molecular physics)

[en] The Fermi surfaces (FS) of LaOFeAs (in k_z = 0 plane) consist of two hole-type circles around Γ point, which do not touch each other, and two electron-type co-centred ellipses around the M point, which are degenerate along the M – X line. By first-principles calculations, here we show that additional degeneracy exists for the two electron-type FS, and the crucial role of F-doping and pressure is to enhance this orbital degeneracy. It is therefore suggested that the inter-orbital fluctuation is important to understand the unconventional superconductivity in these materials

[en] A long-duration gamma-ray burst (GRB) has been widely thought to arise from the collapse of a massive star, and it has been suggested that its ambient medium is a homogenous interstellar medium (ISM) or a stellar wind. There are two shocks when an ultra-relativistic fireball that has been ejected during the prompt gamma-ray emission phase sweeps up the circumburst medium: a reverse shock that propagates into the fireball, and a forward shock that propagates into the ambient medium. In this paper, we investigate the temporal evolution of the dynamics and emission of these two shocks in an environment with a general density distribution of n∝R ^–k (where R is the radius) by considering thick-shell and thin-shell cases. A GRB afterglow with one smooth onset peak at early times is understood to result from such external shocks. Thus, we can determine the medium density distribution by fitting the onset peak appearing in the light curve of an early optical afterglow. We apply our model to 19 GRBs and find that their k values are in the range of 0.4-1.4, with a typical value of k ∼ 1, implying that this environment is neither a homogenous ISM with k = 0 nor a typical stellar wind with k = 2. This shows that the progenitors of these GRBs might have undergone a new mass-loss evolution

[en] The interface effect is taken into consideration, and a special percolation model is proposed for a two-phases metal/ceramic composite in the present paper. The computer simulation shows that the percolation threshold of this interface-controlled percolation behaviour is 4.5% in the three dimensional f.c.c. lattices, which is in good agreement with the experimental data. (author). 9 refs, 3 figs

[en] A class of ceramic composite prepared with two kinds of oxide ceramics of ferroelectric BaTiO₃ and superconducting YBa₂Cu₃O_6+δ was reported, and the phase structure and electrical transport properties of the samples were investigated. The results show that the main phases varied in different composition regions. For low nominal YBa₂Cu₃O_6+δ content, the conductive characteristics of the two phase (BaTiO₃ and YBa₃Ti₂O_8.5) composite follow the three-dimensional percolation model; while for high nominal YBa₂Cu₃O_6+δ contents, superconductivity was observed. (author). 8 refs, 5 figs

[en] A transfer matrix method is developed for optical calculations of non-interacting graphene layers. Within the framework of this method, optical properties such as reflection, transmission and absorption for single-, double- and multi-layer graphene are studied. We also apply the method to structures consisting of periodically arranged graphene layers, revealing well-defined photonic band structures and even photonic bandgaps. Finally, we discuss graphene plasmons and introduce a simple way to tune the plasmon dispersion. (paper)