Structures of amorphous and icosahedral phases in ${\mathrm{Al}}_{75}$${\mathrm{Cu}}_{15}$${\mathrm{V}}_{10}$ and ${\mathrm{Al}}_{53}$${\mathrm{Si}}_{27}$${\mathrm{Mn}}_{20}$ alloys have been studied by x-ray and electron diffraction, and high-resolution electron microscopy. X-ray peak widths of the icosahedral phase in both alloys show a linear dependence on phason momentum. The high-resolution image of the icosahedral phase of ${\mathrm{Al}}_{75}$${\mathrm{Cu}}_{15}$${\mathrm{V}}_{10}$ shows an atomic arrangement similar to that described by the icosahedral-glass (IG) model. The lattice image shows a two-dimensional tiling pattern comprised mainly of pentagons joined together side by side randomly and filled with unique tearlike and cracklike defects exhibited in the IG model. Despite the high degree of structural defects of the IG phase, the characteristic physical properties of quasiperiodic lattices such as high electrical resistivity, high hardness, and large elastic modulus strongly persist in the IG phase.

We have performed positron-annihilation lifetime measurements of the quasicrystalline-phase ${\mathrm{Al}}_{68}$${\mathrm{Mn}}_{20}$${\mathrm{Si}}_4$${\mathrm{Ru}}_8$ and the α-phase ${\mathrm{Al}}_{72.5}$${\mathrm{Mn}}_{17.5}$${\mathrm{Si}}_{10}$. It is suggested that the volume size of the vacant center of the Mackay icosahedron in the quasicrystalline phase is reduced or those centers are occupied with atoms such as manganese.

We propose two different unifications of the Metropolis, the Glauber, and the heat-bath dynamics for the Ising model. Both generalizations satisfy detailed balance. Computer simulations for the d=2 Ising ferromagnetic exhibit, in all cases and for relatively small lattice sizes and simulation times, the expected tendency towards the correct magnetization, specific heat, and susceptibility. The fundamental implications of these results are discussed.

Electrical and magnetic properties have been investigated for (BEDT-TTF)(TCNQ) which is composed of BEDT-TTF sheets and TCNQ columns. The metal-insulator transition temperature ${\mathit{T}}_{\mathrm{MI}}$, 330 K at ambient pressure, decreases down to 40 K by applying hydrostatic pressure, which may be ascribed to the change in both the intermolecular transfer energy and the band filling (molecular valence). Measurements of EPR and magnetic susceptibility indicate that the low-temperature states of BEDT-TTF sheets and TCNQ columns are magnetic insulators, perhaps due to strong electron correlation. An anomalous broadening of EPR linewidth observed below 35 K at ambient pressure suggests an occurrence of magnetic order in BEDT-TTF sheets. A subsequent antiferromagnetic order of TCNQ columns has been found at ${\mathit{T}}_{\mathit{N}}$=3.0±0.1 K from the anisotropic magnetic susceptibility.

Boettger has recently calculated the dependence of iron moments on the spacing in a hexagonal monolayer. Three aspects of his findings are interpreted in tight-binding terms. The overall trend in moments versus spacing is compared to predictions of an Anderson local-moment model. The irregularities are associated with band-edge forms which are specific to a two-dimensional system, and the remarkably low p-like band is seen also to be restricted to two-dimensional systems.

The results of magnetic susceptibility, electrical resistivity, magnetoresistance, and heat-capacity measurements on the nonstoichiometric alloys ${\mathrm{CeFe}}_{\mathit{x}}$${\mathrm{Ge}}_2$ (x=0.53 and 0.63) are reported. Some of the observed properties are typical of (nonmagnetic) Kondo lattices in spite of the nonstoichiometric nature of the chemical composition. These alloys are characterized by a large electronic term in the heat capacity.

Specific heat, magnetic susceptibility, and electrical resistivity have been investigated for moderately dilute ${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Cu}}_{2.2}$${\mathrm{Si}}_2$ alloys (x≤0.2) between 1 and 20 K. ${\mathrm{Ce}}_{0.1}$${\mathrm{La}}_{0.9}$${\mathrm{Cu}}_{2.2}$${\mathrm{Si}}_2$ has been found to possess a logarithmic temperature variation in C/T and χ, implying a possibility of the two-channel Kondo effect. However, magnetic-field dependence of C is not consistent with such an interpretation. Anomalous spin-glass-like behavior observed for related ${\mathrm{Ce}}_{0.15}$${\mathrm{La}}_{0.85}$${\mathrm{Cu}}_{2.2}$${\mathrm{Si}}_2$ at low temperatures indicates a magnetic nature of the phenomenon.

Infinite-temperature long-time dynamics of Heisenberg model H^=-1/2${\mathit{tsum}}_{\mathit{i},}$${\mathit{jJ}}_{\mathit{i}\mathit{j}}$S${\mathrm{^}}_{\mathit{i}}$⋅S${\mathrm{^}}_{\mathit{j}}$ is investigated. It is shown that the quantum-spin pair correlator is equal to the correlator of a classically evaluated vector field averaged over the initial conditions with respect to the Gaussian measure. In the continuous-limit case, the scaling estimations allow one to find the one-point correlator that turns out to be C(r=0;t)∝const×${\mathit{t}}^{\mathrm{-}6/7}$. All results are obtained by straightforward procedures without any assumptions of the phenomenological character.

A next-nearest-neighbor hopping t’ in the t-t’-J model has a different sign between the hole- and electron-doped systems of high-${\mathit{T}}_{\mathit{c}}$ cuprates: t’<0 for the hole-doped system and t’>0 for the electron-doped system. We show that the sign is responsible for the remarkable difference of antiferromagnetic (AF) phases between the two systems. To reveal this and clarify the role of t’, we examine magnetic excitations of the t-t’-J model by employing exact diagonalization techniques for 4×4 and √18 × √18 lattices. In the low-doping region (two-hole case of the √18 × √18 lattice), AF spin correlations are stabilized for the case of t’>0, i.e., electron-doping case, but not for the case of t’<0. In the high-doping region (four-hole case of the 4×4 lattice and more) magnetic excitations are mainly controlled by the geometry of the Fermi surface of the noninteracting system.

Phonon transmission through superconducting In, Sn, and Pb films (with thicknesses of 4 and 8 μm) is studied with a heat-pulse technique using a semiconductor Si:P detachable bolometer as the phonon detector. Below the critical temperature of the films, ballistic-phonon propagation is observed. From the dependence of the phonon transmission on the incident power and film thickness, we calculate the mean free path of phonons at the gap frequency. The phonon transmission amount changes when a magnetic field is applied and is also different if the field is parallel or perpendicular to the film. By a simple model based on the Landau laminar model for intermediate states, the critical field for the films can be calculated. Good agreement (for In and Sn) with the theoretical values is obtained.

Displaced squeezed states are proposed as variational ground states for phonons (Bose fields) coupled to two-level systems (spin systems). We have investigated the zero-temperature phase diagram for the localization-delocalization transition of a tunneling particle interacting with an Ohmic heat bath. Our results are compared with known existing approximate treatments. A modified phase diagram using the displaced squeezed state is presented.

We report on measurements of the penetration of magnetic flux in single crystals of (${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${)}_2$${\mathrm{CuO}}_4$ as seen using the magnetic garnet imaging technique. The technique measures the spatial and temporal dependence of the magnetization by using a wafer of doped magnetic garnet material placed in contact with the sample to be measured and imaged with an optical microscope. We have directly measured the critical current anisotropy in this system as a function of temperature and doping and found clear evidence for intrinsic pinning as well as a pronounced dependence of the anisotropy on doping.

The NMR relaxation rate in the Hubbard model in high dimensions is investigated. First, by an analysis of the response functions, it is shown that, in the infinite-dimensional models, the intersite correlation does not directly affect the local response of the system. A simple approximation to consider the effects of the finite dimensions is then presented, and effects of the antiferromagnetic (AF) correlation on the NMR relaxation rate in the finite-dimensional Hubbard model is studied by treating the interaction by the self-consistent second-order perturbation theory. It is found that at low temperatures the AF correlation seriously affects the temperature dependence of the NMR relaxation rate in contrast to the case in the infinite dimensions.

We analyze the center-of-mass order parameter in s-wave and d-wave superconductors and find a large spatial dc term in the s wave but none in the d wave. Thus, the d-wave hypothesis may reconcile high-temperature superconductivity with Hohenberg’s theorem. The center-of-mass order parameter has nodes at Cu sites and peaks at O sites with opposite signs at x- and y-bonded oxygens. At boundaries, it attains opposite amplitudes for x and y edges. A singular Ginzburg-Landau parameter at ${\mathit{T}}_{\mathit{c}}$ is predicted, which suggests that the maximum energy gap opens quickly.

We report measurements of the superconducting transition temperature in a compound with a nominal composition ${\mathrm{Cs}}_{2.5}$${\mathrm{Rb}}_{0.5}$${\mathrm{C}}_{60}$ under hydrostatic pressure of up to 15.5 kbars. We observe two transitions, at temperatures ${\mathit{T}}^{\mathrm{*}}$ and ${\mathit{T}}_{\mathit{c}}$ in this pelletized sample. We identify the lower temperature transition ${\mathit{T}}^{\mathrm{*}}$ with the onset of intergranular shielding currents. The upper transition temperature ${\mathit{T}}_{\mathit{c}}$(P) falls on a universal ${\mathit{T}}_{\mathit{c}}$(P) curve, defined from similar data obtained previously on ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3$${\mathrm{C}}_{60}$, after we shift the pressure axis for our data by -2.6 kbars. We identify ${\mathit{T}}_{\mathit{c}}$ as a superconducting transition in ${\mathrm{Rb}}_2$${\mathrm{CsC}}_{60}$ on the basis of the compressibility analysis and published values of the lattice parameters for alkali-doped ${\mathrm{C}}_{60}$, as well as ${\mathit{T}}_{\mathit{c}}$(P=0) and (${\mathit{dT}}_{\mathit{c}}$/dP${)}_{\mathit{P}=0\mathrm{}}$.

A linear rate law has been derived for the final stages of decay of the excess surface area of a spheroidal solid particle approaching a spherical shape. Solid-state diffusion within the particle, driven by stress gradients resulting from nonsphericity, is assumed to be the controlling mechanism. The derivation is based on a solution to Laplace’s equation for the chemical potential inside the solid particle, which satisfies the boundary condition for the chemical potential on the particle surface. The characteristic frequency for the decay is 16${\mathit{v}}_{\mathit{m}}^2$Lσ/${\mathit{R}}^3$ where ${\mathit{v}}_{\mathit{m}}$ is the molecular volume, σ the surface tension, and R the radius of the sphere. The phenomenological coefficient L appears in the diffusional flux, driven by the chemical-potential gradient.

We report the observation of perpendicular magnetization in ultrathin amorphous ${\mathrm{Fe}}_{70}$${\mathrm{B}}_{30}$/Ag multilayer films by means of Mössbauer spectroscopy. In contrast to other techniques that require the application of an external magnetic field, the field-free condition of Mössbauer spectroscopy allowed the intrinsic magnetic properties of ultrathin films to be studied. Our study indicates that at elevated temperatures an external field may easily alter the spontaneous magnetization in an ultrathin film with very small effective anisotropy and thus obscure its intrinsic magnetic properties. By virtue of the microscopic probing capability of Mössbauer spectroscopy, the surface magnetic properties of thin amorphous ${\mathrm{Fe}}_{70}$${\mathrm{B}}_{30}$ films have also been studied.

A generalization of the t-J model in a system of two coupled chains or planes is studied by numerical diagonalization of small clusters. In particular, the effect of density fluctuations between these one- or two-dimensional coupled layers on intralayer phase separation and pairing is analyzed. The most robust signals of superconductivity are found at quarter filling for couplings just before the fully interlayer phase separated regime. The possibility of an enhancement of the intralayer superconducting pairing correlations by the interlayer couplings is investigated.

All magnetic anisotropy contributions in single-crystalline (1 1 13)-oriented Co films on Cu were determined at room temperature using Brillouin light scattering. An in-plane uniaxial anisotropy contribution, not found in the reference system Co/Cu(001), is identified as magnetoelastic in origin. From the thickness dependence of the in-plane anisotropies of both twofold and fourfold symmetry about the film normal it is concluded that elastic strain fields are very likely to provide the driving mechanism for stabilizing ferromagnetic order in ultrathin Co(1 1 13) films.

The anisotropic local structure in a series of amorphous ${\mathrm{Tb}}_{26}$${\mathrm{Fe}}_{74}$ films deposited at different deposition temperatures and having different magnetic anisotropy energies have been investigated using polarization-dependent extended x-ray-absorption fine-structure measurements. Samples deposited at temperatures ≥300 K exhibit anisotropic pair correlations where like atomic pairs are favored in plane and unlike pairs are favored out of plane. Both the anisotropic pair correlations and the perpendicular magnetic anisotropy increase with increasing deposition temperature. In contrast, a sample deposited at 77 K was found to have isotropic pair correlations, low perpendicular magnetic anisotropy, and a large (≊1%) in-plane compression.