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A U(3) model proposed by Iachello for superconductivity in cuprate materials is analyzed. The model consists of s and d pairs (approximated as bosons) in a two-dimensional Fermi system with a surface. The transition occurs between a phase in which the system is a condensate of one type of boson, and a phase which is a mixture of two types of bosons. In the current work we have investigated the validity of the Bogoliubov approximation, and we used a reduced Hamiltonian to determine a phase diagram, the symmetry of the phases, and the temperature dependence of the heat capacity. [ABSTRACT FROM AUTHOR]

High temperature superconducting copper oxides (HTSC) have been shown to be intrinsically heterogeneous. Consequently multiple ground states coexist, which are either in competition with or of support to superconductivity. Here it is shown that spin, charge and lattice are intrinsically coupled to form a composite of locally charge carrying distorted areas in an antiferromagnetic matrix on the regular lattice. The dynamical interplay between both induces level shifts together with band narrowing of the spin and charge related bands, by means of which interband interactions are possible which lead to a substantial increase in the superconducting transition temperature T c . Further consequences of this multicomponent approach as, for example, isotope effects are discussed. [ABSTRACT FROM AUTHOR]

The long-time (hundreds of hours) reversible changes of the temperature dependences of the YBa2Cu3O7-x ceramic resistance, induced by a short-time (seconds) action of comparatively weak (≤ 5kOe) pulsed magnetic fields, have been found out. The effect is explained by a transition of the oxide-based superconductor from the normal metallic state into the pseudo-gap regime as a result of the partial loss of oxygen atoms from Cu─O chains. [ABSTRACT FROM AUTHOR]

Direct measurements of the in-plane London penetration depth λ L have recently been performed on high-temperature superconducting copper oxides by a new low-energy muon spin rotation technique. The results show that λ L is isotope dependent, evidencing unconventional electron-phonon interactions as its source. The data are interpreted here in terms of polaronic effects on the single-particle energies, which leads to level shifts and exponential band narrowing. Good agreement with the experimental data is obtained. [ABSTRACT FROM AUTHOR]

Recent data from angle-resolved photoemission experiments published by Zhou et al . [ Nature , 423 , 398 (2003)] concerning a number of hole-doped copper-oxide-based high-temperature superconductors reveal that in the nodal directions of the underlying square Brillouin zones (i.e. the directions along which the d-wave superconducting gap is vanishing) the Fermi velocities for some finite range of k inside the Fermi sea and away from the nodal Fermi wave vector k F are to within an experimental uncertainty of approximately 20% the same both in all the compounds investigated and over a wide range of doping concentrations and that, in line with earlier experimental observations, at some characteristic wave vector k ☆ away from k F ( typically amounts to approximately 5% of ) the Fermi velocities undergo a sudden change, with this change (roughly speaking, an increase for ) being the greatest (smallest) in the case of underdoped (overdoped) compounds. We demonstrate that these observations establish four essential facts: firstly, the ground-state momentum distribution function must be discontinuous at k = k ☆ ; with and denoting the measured velocities close to and , we obtain in which is the 'Fermi' velocity corresponding to the case in which (for two-body interaction potentials of shorter range than the Coulomb potential, whereby ); secondly, the single-particle spectral function must at k = k ☆ possess a coherent contribution corresponding to a well-defined quasiparticle excitation at an energy of approximately 70 meV below the Fermi energy; thirdly, the amount of discontinuity in at the nodal Fermi points must be small and ideally vanishing; fourthly, the long range of the two-body Coulomb potential is of vital importance for realization of a certain aspect of the observed behaviour in the Fermi velocities (specifi- cally) in the underdoped regime. The condition conforms with the observation through an earlier angle-resolved photoemission experiment by Valla et al . [ Science , 285 , 2110 (1999)], on the optimally doped compound Bi 2 Sr 2 CaCu 2 O 8 + δ , which shows that the imaginary part of the self-energy along the nodal directions of the Brillouin zone and in the vicinity of the nodal Fermi points satisfies the scaling behaviour characteristic of marginal Fermi-liquid metallic states, for which is indeed vanishing. We present arguments advocating the viewpoint that the observed 'kink' in the measured energy dispersions cannot be a direct consequence of electron-phonon interaction, although a finite may possibly arise from this interaction. In other words, even though possibly vital, the role played by phonons in bringing about the latter 'kink' must be indirect. Our approach further provides a consistent interpretation of the observed sudden decrease in the width of the so-called 'momentum distribution curve' on | k | increasing above . [ABSTRACT FROM AUTHOR]

Cathodoluminescence measurements are obtainable from the surface of (Bi,Pb)-2223/Ag superconductor tape. The beam position, and hence intensity and spectra, respond to superconducting changes in the core material. Thus they provide not only a direct measurement of the superconducting transition temperature, but also evidence for granular variations in the transition temperature. Extension of the method for more general application and imaging of structure from grains or field patterns is discussed. [ABSTRACT FROM AUTHOR]

Electronic states of copper oxides were investigated after hole-doping by using Hybrid-DFT (UB2LYP) calculations for three types of model clusters. Energy diagram in hole-doped state is explained by using d-p interaction between 3d x 2 -y 2 orbital of copper and 2p orbital of oxygen and superexchange interaction (SE) between copper orbitals via closed oxygen orbital. Copper oxides Hole-doping Density Functional Theory (DFT) CASSCF Superexchange (SE) interaction Superconductivity [ABSTRACT FROM AUTHOR]

We review recent results for the properties of doped antiferromagnets, obtained by the numerical analysis of the planar t-J model using the novel finite-temperature Lanczos method for small correlated systems. First we briefly summarize our present understanding of anomalous normal-state properties of cuprates, and present the electronic phase diagram, phenomenological scenarios and models proposed in this connection. The numerical method is then described in more detail. The following sections are devoted to various static and dynamical properties of the t-J model. Among the thermodynamic properties the chemical potential, entropy and the specific heat are evaluated. Discussing electrical properties the emphasis is on the planar optical conductivity and the d.c. resistivity. Magnetic properties involve the static and dynamical spin structure factor, as measured via the susceptibility measurements, the NMR relaxation and the neutron scattering, as well as the orbital current contribution. The analysis of electron spectral functions, studied by photoemission experiments, and their relation to the c-axis conductivity, follows. Finally we discuss density fluctuations, the electronic Raman scattering and the thermoelectric power. Whenever feasible a comparison with experimental data is performed. A general conclusion is that the t-J model captures well the main features of anomalous normal-state properties of cuprates, for a number of quantities the agreement is even a quantitative one. It is shown that several dynamical quantities exhibit at intermediate doping a novel universal behaviour consistent with a marginal Fermi-liquid concept, which seems to emerge from a large degeneracy of states and a frustration induced by doping the antiferro magnet. [ABSTRACT FROM AUTHOR]

This research is concerned with Y[sub 1]Ba[sub 2]Cu[sub 3]O[sub 7−δ] superconductor ceramics. This ceramic pressed into a cylindrical form was cut into a wire coil by manual work and the Q-value as against frequency was measured in parallel resonance of a 5 turn coil. When the coil was cooled below the critical temperature, the electrical resistance of the superconductor vanished and the Q-value increased by about 9 times from 13 to 112 for a parallel capacity of 100 pF. The inductance of the coil was about 0·201 μH for a frequency of 25·2 MHz. [ABSTRACT FROM AUTHOR]

I argue that Anderson's identification of the conflict between the fermi-liquid and non-fermi-liquid metallic states as the central issue of cuprate superconductivity is fundamentally wrong. All experimental evidence points to adiabatic continuability of the strange metal into a conventional one, and thus to one metallic phase rather than two, and all attempts to account theoretically for the existence of a luttinger-liquid at zero temperature in spatial dimension greater than one have failed. I discuss the underlying reasons for this failure and then argue that the true higher-dimensional generalization of the luttinger-liquid behavior is a propensity of the system to order. This implies that the central issue is actually the conflict between different kinds of order, i.e. exactly the idea implicit in Zhang's paper. I then speculate about how the conflict between antiferromagnetism and superconductivity, the two principal kinds of order in this problem, might result in both the observed zero-temperature phase diagram of the cuprates and the luttinger-liquid phenomenology, i.e. the breakup of the electron into spinons and holons in certain regimes of doping and energy. The key idea is a quantum critical point regulating a first-order transition between these phases, and toward which one is first attracted under renormalization before bifurcating between the two phases. I speculate that this critical point lies on the insulating line, and that the difference between the Mott-insulator and fermi-liquid approaches to the high TC problem comes down to whether or not the superconducting states made by nand p-type doping can be continued into each other. A candidate for the second fixed point required for distinct superconducting phases is the P- and T-violating chiral spin liquid state invented by me. [ABSTRACT FROM AUTHOR]