The magnetization curves and phase, field, and current-density profiles for uniform Josephson junctions (JJs) with length 2L are calculated from the sine-Gordon equation. It is found that M starts to be a multivalued function of H at l≡L/${\lambda }_{\mathit{J}}$=${\mathit{l}}_{\mathit{c}}$=1.995, ${\lambda }_{\mathit{J}}$ being the Josephson penetration depth; when l>${\mathit{l}}_{\mathit{c}}$, increasing and decreasing H will cause M to jump so that hysteresis loops are formed; the hysteresis loops of very long JJs with l≫${\mathit{l}}_{\mathit{c}}$ have a shape similar to that of type-II superconductors (SC2s) with a surface barrier but both have quantitative differences; being cooled in a constant field, JJs show a Meissner effect distinct from that of SC2s. These results are explained in terms of Josephson vortices. One of the most fundamental differences between JJs and SC2s is that there is a surface current separated from the vortices for the latter but not for the former.

This paper discusses some intriguing questions regarding the covariant Landau theory of Fermi liquids. One question is why this theory, with its off-shell distribution function, is an exact reformulation of classical Landau theory. Other questions address some remarkable properties of covariant Landau theory and its extensions.

The H-T phase diagram of ${\mathrm{UPt}}_3$ has previously been shown to be incompatible with a two-component-vector order parameter. It is studied in this paper within the ‘‘AB’’ model, consisting of two nearly degenerate order parameters, one transforming as an A and the other as a B representation of ${\mathit{D}}_{6\mathit{h}}$. The nature of the different one- and two-order-parameter vortex-lattice phases and the possible transitions between them are examined in detail. A quantitative comparison is made with the experimental diagram, and the parameters in the Ginzburg-Landau free energy are deduced. It is found that the flux lattice evolves continuously in the low-H, low-T phase with no additional transitions between different types of two-order-parameter lattices, and that its orientation is in accord with neutron-diffraction studies near one of the inner transition lines.

The rate at which dissipative fluctuations occur in narrow superconducting rings is considered within the Little-Langer-Ambegaokar-McCumber-Halperin framework. The mesoscopic regime, in which the ring circumference L does not greatly exceed the correlation length ξ, is specifically addressed. In this regime, significant differences arise between models that mimic voltage and current sources, the former (latter) exhibiting corrections to the fluctuation rate algebraic in ξ/L (exponentially small in L/ξ). The theory employs Forman’s elaboration of the Gel’fand-Yaglom technique for computing fluctuation determinants.

The dc Josephson effect of a superconductor/two-dimensional electron gas/superconductor (S/2DEG/S junction in the clean limit is investigated with emphasis on the field-effect dependence of the critical current. Calculation of the Josephson current is based on solving the Bogoliubov–de Gennes equations for a steplike variation of the pair potential. In the normal conducting region, the motion of electrons is quantized in one direction by means of a triangular-well potential. The 2DEG is contained in a semiconductor treated within the effective-mass approximation. We assume an abrupt band-edge jump at the interfaces, and additional scattering is taken into account by δ-function potential barriers. Normal scattering leads to the formation of resonant states, which are visible in critical current oscillations. The ratio of Fermi velocities in the 2DEG and the S regions determines the rates of Andreev and normal scattering and has a large influence on the field-effect dependence of the critical current. We take an effective mass suitable for the inversion layer on p-type InAs and consider Nb for the superconducting contacts. Typical magnitudes of the calculated critical current are some μA-per-μm junction width for experimentally accessible values of junction length, temperature, and surface carrier density of the 2DEG.

We have studied the three-band Peierls-Hubbard model describing the Cu-O layers in high-${\mathit{T}}_{\mathit{c}}$ superconductors by using Lanczos diagonalization and assuming infinite mass for the ions. When the system is doped with one hole, and for λ (the electron-lattice coupling strength) greater than a critical value, we found that the oxygens around one Cu contract and the hole self-traps forming a lattice and electronic small polaron. The self-trapped hole forms a local singlet analogous to the Zhang-Rice singlet in the undeformed lattice. We also studied the single-particle spectral function and the optical conductivity. We have found that the spectral weight, in general, is similar to that found in previous studies where the coupling with the lattice was absent. There is an anomalous transfer of spectral weight but, contrary to those studies, the spectral weight goes to these localized polaronic states. However, this polaronic shift does not seem enough by itself to explain pinning of the chemical potential observed in real materials. The peaks in the optical conductivity are also shifted, according to the polaronic shift, in the single-particle spectral functions. We compare our results to those obtained in inhomogeneous Hartree-Fock calculations and we discuss their relation with experiments.

A lattice-gas model for the high-temperature oxygen-ordering thermodynamics in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ is presented, which assumes constant effective pair interactions between oxygen atoms and includes in a simple fashion the effect of the electron spin and charge degrees of freedom. This is done using a commonly utilized picture relating the creation of mobile electron holes and unpaired spins to the insertion of oxygen into the basal plane. The model is solved using the nearest-neighbor square approximation of the cluster-variation method. In addition, preliminary Monte Carlo results using next-nearest-neighbor interactions are presented. The model is compared to experimental results for the thermodynamic response function, kT(∂x/∂μ${)}_{\mathit{T}}$ (μ is the chemical potential), the number of monovalent copper atoms, and the fractional site occupancies. The model drastically improves the agreement with measured values of kT(∂x/∂μ${)}_{\mathit{T}}$ as compared to bare lattice-gas models. Additionally, the monovalent copper count, in contrast to the standard lattice-gas models, is determined self-consistently and agrees qualitatively with experiment.

The electronic structure of the ${\mathrm{CuO}}_{\mathit{x}}$ planes is studied using a generalized Hubbard model including Cu-O repulsion ${\mathit{U}}_{\mathit{p}\mathit{d}}$, for each value of x and two different assumptions on the oxygen (O) ordering. The result explains qualitatively the experimentally observed hole count in the ${\mathrm{CuO}}_2$ planes, the amount of ${\mathrm{Cu}}^{+}$ and the metal-insulator transition near x=0.5. For large enough ${\mathit{U}}_{\mathit{p}\mathit{d}}$, the energy ΔE favoring ordering in chains is positive. A simple explanation of this and the relation between charge transfer and O ordering is given. The screening length λ is calculated using Thomas-Fermi theory, an effective one-band model for the ${\mathrm{CuO}}_2$ planes and experimental data. This information is used to construct an effective lattice-gas model for the O ordering, based on O-O screened repulsions in which ΔE is the only parameter. The superstructures predicted by this model provide an explanation of almost all observed diffraction patterns and of recently observed photoinduced changes in the transport properties. The electronic and structural results are consistent with the observed dependence of the superconducting ${\mathit{T}}_{\mathit{c}}$ vs x.

We present results of inelastic-neutron-scattering, specific-heat, and susceptibility measurements of ${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, where a transition from superconductor to an antiferromagnetic insulator with increasing Pr concentration occurs. The inelastic-neutron-scattering spectra confirm the prediction of the crystal-field (CF) splitting of the J=4 Hund’s-rule ground state, based on the superposition model: a ‘‘quasitriplet’’ ground state and six further singlets at energies larger than 60 meV. The local susceptibility extracted directly from the magnetic neutron spectra is in good agreement with the bulk susceptibility for both ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ and ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$. Moreover we show that the experimental specific-heat and susceptibility data can be interpreted consistently in terms of the standard crystal-field theory of ${\mathrm{Pr}}^{3+}$ based on the CF parameters extracted from the neutron data via the superposition model.

We present a theoretical treatment of the ${\mathit{D}}_{\mathit{h}\mathit{d}}$ phase of a one-dimensional chiral discotic liquid crystal of ${\mathit{D}}_3$ symmetry molecules. This model is shown to reduce to a one-dimensional classical chiral planar model in a twofold anisotropy field. The thermodynamic properties and correlation functions are calculated numerically using the transfer-matrix method. Analytical results are obtained in the isotropic limit. The thermal expansion coefficient is shown to change sign at low temperature. The specific heat shows a crossover from the intrinsic planar character to an Ising-like behavior at low temperature.

The basic equations of the presented model are the Maxwell heat-conduction equation, the kinetic equation for the thermally activated carriers in Fermi glasses, and the Gauss equation. Assuming, that the temperature and the concentration of the thermally activated carriers may be divided into equilibrium and nonequilibrium parts and that the electric field consists of constant and variable parts, the system of equations is linearized. It is shown that it possesses solutions in the form of nondamped self-consistent temperature waves (STW’s) similar to second-sound waves. These solutions are analyzed and it is shown that STW’s exist down to some limiting frequency. Numerical calculations are performed for the Fermi-glass phase of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$.

We present an experimental study of the dimensional crossover present in the extremely anisotropic superconductor ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathit{x}}$ by means of measurements of the onset field for the dissipation ${\mathit{H}}^{\mathrm{*}}$ as a function of the temperature and of the orientation ϑ between the field direction and the a,b plane. The crossover is experimentally shown to depend on the strength of the applied magnetic field in a narrow temperature range below ${\mathit{T}}_{\mathit{c}}$. The entire set of experimental data is described by a coupled-layers model, in which a decoupling can be induced by a sufficiently high magnetic field. The anisotropy ratio is found to depend strongly on the temperature and the model of coupled slabs of finite thickness quantitatively describes the data.

The published structure of ${\mathrm{La}}_2$${\mathrm{NiO}}_{4+\mathit{y}}$ has unusually short (1.94 Å) Ni-O bond lengths. We reexamined the structure of ${\mathrm{La}}_2$${\mathrm{NiO}}_{4.18}$ using monochromatic synchrotron x-ray radiation. Rietveld refinement of the structure in space group Bbcm yielded Fourier synthesis (${\mathit{F}}_{\mathrm{obs}}$) maps that suggest a modified structural model for ${\mathrm{La}}_2$${\mathrm{NiO}}_{4.18}$. The refined structure contains chemically more reasonable interatomic distances (e.g., shortest Ni-O distance of 2.00 Å). A comparison of this structure with that of the superconductor ${\mathrm{La}}_2$${\mathrm{CuO}}_{4+\mathit{y}}$ reveals disparities in the conduction planes of the two materials that may explain differences in electrical behavior.

Fluctuation analysis in the limit of high magnetic fields was performed on three epitaxial thin films of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ for various oxygen deficiencies δ<0.3. On the 90-K plateau, the three-dimensional (3D) limit yielded an ${\mathit{H}}_{\mathit{c}2}$(T) slope of -1.7 T/K for H∥c, consistent with previous observations of transport and magnetic properties. Moreover, the 3D scaling showed better convergence than the 2D scaling, which gave relatively low values of ${\mathit{H}}_{\mathit{c}2}$. In contrast, the transitions were not adequately described by either scaling for ${\mathit{T}}_{\mathit{c}}$ off the 90-K plateau; it is speculated that this is due to an extrinsic broadening of the transitions, possibly due to the lack of a complete percolation path of the ortho-I phase (δ=0).

We have measured the normal-state Hall effect on single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_{3\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ with the magnetic field perpendicular to the ab plane and the current in the ab plane. The Hall coefficient is positive for all crystals (0≤x≤0.20) over the entire temperature range of our measurement (${\mathit{T}}_{\mathit{c}}$≤T≤300 K). A strong temperature dependence of the Hall coefficient was also observed. We show that the Hall angle in the normal-state follows the relation cot ${\mathrm{FTHETA}}_{\mathrm{H}}$=${\mathrm{AT}}^2$+B, which is in agreement with Anderson’s prediction for the two-dimensional Luttinger liquid.

For ${\mathrm{Gd}}_2$${\mathrm{CuO}}_4$, a symmetry-forbidden phonon for the tetragonal T’ structure is observed. This shows that oxygen in the ${\mathrm{CuO}}_2$ plane is locally distorted along the plane. Such distortion has not been observed for other T’-type superconductors. The normal-mode calculation shows that the correlation between the ${\mathrm{CuO}}_2$ plane and R-O layers increases with decreasing ionic radius. The increased three-dimensional character and the appearance of the distortion of O in the ${\mathrm{CuO}}_2$ plane along the a axis are useful experimental results that help clarify the mechanism that causes the disappearance of superconductivity for Gd.

A group of analytical wave functions is confirmed to be the ground state of a Hubbard model on a double-layer square lattice in the case of half-filling and in the case with one or two doped holes for a range of parameters. The method is based on the variational principle, and no approximations are applied. In the case of half-filling, the ground state is a product of local pairs. In the case of one or two holes, the doped holes are freely moving in the above background. In both cases there exists a long-range order of the evenness and oddness with respect to the layer parity.

Synchrotron-excited angle-resolved photoemission data for a cleaved single-crystal ${\mathrm{BaPb}}_{0.81}$${\mathrm{Bi}}_{0.19}$${\mathrm{O}}_3$ (001) surface are presented. Enhancements in spectral intensity at the Fermi energy away from the Γ point are shown to be in reasonable agreement with linear-augmented-plane-wave band-structure calculations [Phys. Rev. B 28, 4227 (1983)]. The rapid surface degradation of metallic and superconducting compositions in the ${\mathrm{BaPb}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Bi}}_{\mathit{x}}$${\mathrm{O}}_3$ system is discussed.

c-axis-oriented ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ (1:2:3) and ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ (1:2:4) thin films were charged with hydrogen at 463 K and a ${\mathrm{H}}_2$ pressure of 100 mbar. The hydrogen concentrations and depth profiles were measured with the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ nuclear reaction method. In contrast to earlier studies on bulk samples where a constant ${\mathit{T}}_{\mathit{c},\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{e}\mathrm{t}}$ is reported, we find in our 1:2:3 films that the superconducting transition temperature decreases continuously with increasing hydrogen concentration and that the transitions remain relatively sharp, e.g., ${\mathit{T}}_{\mathit{c},\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{e}\mathrm{t}}$=38 K and Δ${\mathit{T}}_{\mathit{c}}$=6.2 K for [H]/cell≃0.6. The electrical resistivity and Hall-effect measurements in the normal state indicate that the main effect of hydrogen doping is a reduction of the charge carrier concentration, whereas the carrier mobility is not changed significantly. At an average hydrogen concentration of [H]/cell≃2 in both systems, a new hydride phase is observed, which for 1:2:3 is characterized by a c-axis expansion of 16% and for 1:2:4 by a c-axis expansion of 1.5%.

A generalized slave-particle scheme is introduced to study the t-J model with nonlocal effects included. A charge-spin decoupled state is found in this scheme, in which the nonlocal gauge fields play a role of attaching fictitious quantized fluxes to the particles as an effective way to describe antiferromagnetic correlation. As a result, the gauge fluctuation is suppressed in the long-wavelength limit, which shows the stability of flux binding, and the electromagnetic response function of such a state exhibits the Meissner effect. An important consequence of the present approach is that the electron, as a combination of the charge and spin degrees of freedom, does not show time-reversal and parity-symmetry-broken behavior, in contrast to the usual anyon theory. This is consistent with experimental results. The robustness of this conclusion relies on the exactness of the constraint between the charge and spin degrees of freedom as well as the flux binding condition. We also calculate the momentum distribution of electrons, which shows a characteristic scale equal to the Fermi momentum ${\mathit{k}}_{\mathit{f}}$.