Seebeck coefficients of ${\mathrm{BaBi}}_{0.25}$${\mathrm{Pb}}_{0.75}$${\mathrm{O}}_{3\mathrm{-}\mathrm{\delta }}$ (0.00≤δ≤0.08) were measured as a function of temperature up to 1100 K in various ${\mathrm{O}}_2$ partial pressures. The Seebeck coefficient of ${\mathrm{BaBi}}_{0.25}$${\mathrm{Pb}}_{0.75}$${\mathrm{O}}_{3.00}$ below 300 K was negative by a few μV/K and showed linear temperature dependence, indicating a metallic or semimetallic nature of the carrier electrons. Above 300 K, the Seebeck coefficient (δ=0.00) increased, becoming positive around 400 K. Curve fitting with an assumption of the coexistence of electrons that show delocalized character and holes that have a localized nature was carried out to determine the relationship between the Seebeck coefficients and the temperature of the sample. The temperature dependence of not only the Seebeck coefficient but also the electrical conductivity of the sample could be well explained by the assumption described above. From the comparison with electronic-band calculations, it is deduced that electrons with high mobility and holes with low mobility are the product of delocalized bands composed of Pb(Bi) 6s and O 2p antibonding orbitals and localized bands composed of O 2p isolated orbitals, respectively. The Seebeck coefficients of the samples with δ values of 0.025–0.08 were also slightly negative at low temperatures and had values of ∼20 μV/K at around 1100 K. Finally, it could also be deduced that electrons and holes existed simultaneously in samples with an oxygen deficiency.

Pronounced effects of a surface barrier are frequently observed on polycrystalline superconductors of ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{2\mathit{n}+2+\mathrm{\Delta }}$ [Hg-12(n-1)n] with n=1, 2, and 3. Compared with other known high-temperature superconductors, the effects at low temperatures are much stronger and persist over a wide range of magnetic fields. The present analysis shows that the enhancement of the irreversible magnetization of grains by the surface barrier is comparable to that by neutron irradiations. The magnitude of the surface supercurrent density is >4×${10}^7$ A/${\mathrm{cm}}^2$ at T=40 K and H=45 kG, for Hg-1223. The upper and lower boundaries of the thickness of the vortex-free region and the surface-current density are analyzed as functions of temperature and field.

Bistable hydrogen bonds are shown to induce systematic displacements in arrangement of molecules or ions in the structures of ferroelectric crystals: methods of calculating the magnitudes of the displacements, and characteristic structural transformations on disordering of the H atom above ${\mathit{T}}_{\mathit{c}}$ are described. The displacements are correlated with ${\mathit{T}}_{\mathit{c}}$, and their contribution to the isotope effect on ${\mathit{T}}_{\mathit{c}}$, and to the differences in ${\mathit{T}}_{\mathit{c}}$ between isostructural ferroelectric crystals are discussed.

Raman spectra of ${\mathrm{LiCsSO}}_4$ were performed for pressures up to 13.5 GPa. Several modifications in the spectra are interpreted as due to a structural phase transition occurring at 3.8 GPa. This transition is reversible and both directions are fast, in agreement with the general criteria for polyhedral tilt transitions. Pressure coefficients of Raman modes are given.

The crystal structure of arsenic has been studied in a diamond anvil cell by energy dispersive x-ray diffraction with a synchrotron source to 122 GPa, where V/${\mathit{V}}_0$=0.513. The phase sequence on compression is: α→sc→As(III)→bcc. As(III) may have the α-Np structure. The equilibrium transformation pressures, ${\mathit{P}}_{\mathit{e}}$, between sc/As (III) and As(III)/bcc are 48±11 and 97±14 GPa, respectively. There is no measurable volume discontinuity between the phases. The equation of state was measured and the BE2 parameters are in good agreement with literature values.

The phase relation of the La-Co-Si ternary system in the La-poor region (≤25 at. % La) was determined by means of x-ray powder diffraction. In this region there exist four ternary compounds: ${\mathrm{LaCoSi}}_3$, ${\mathrm{LaCoSi}}_2$, ${\mathrm{LaCo}}_2$${\mathrm{Si}}_2$, and ${\mathrm{LaCo}}_{13\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$. The cubic ${\mathrm{LaCo}}_{13\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ intermetallic compound with ${\mathrm{NaZn}}_{13}$-type structure could be changed to a tetragonal one with ${\mathrm{NaZn}}_{13}$-derivative structure by vacuum annealing after arc melting. The tetragonal ${\mathrm{LaCo}}_{13\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ compounds can exist stably in the composition range between x=2.0 and 5.0. The space group of the tetragonal ${\mathrm{LaCo}}_{13\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ intermetallic compound is I4/mcm. The crystal structure of the tetragonal phase was refined by the Rietveld method. Si atoms show a strong preference for occupying a specific crystallographic position in the structure; i.e., atomic ordering occurs. Magnetic measurements indicate that the tetragonal ${\mathrm{LaCo}}_{13\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ intermetallic compounds are ferromagnetic with Curie temperature higher than 900 K and anisotropy fields of about 10 kOe. The saturation magnetic moment per Co atom in the tetragonal ${\mathrm{LaCo}}_{13\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ compounds decreases with Si content. The composition dependence of the saturation magnetic moment per Co atom can be satisfactorily explained by the rigid-band model.

We describe a manifestation of diffractive behavior in diffusion in a porous medium: the measured magnetization M(q,t), in a pulsed field gradient NMR spin-echo experiment on fluid molecules confined in a porous medium, is proportional to Γ(t)(S/${\mathit{V}}_{\mathit{p}}$)${\mathit{q}}^{\mathrm{-}4}$ for large q, in analogy with the Debye-Porod law. The time-dependent function Γ(t) starts out with a value of 2 for short t and approaches, for connected porous media, unity for large t. Experiments on two different suspensions of beads of known sizes, in the 500 and 50 μm range, respectively, show that Γ(t) lies between 2 and 1 in the intermediate-time regime. We argue that for more complex porous media Γ(t) can be outside these limits at intermediate times, and can be used as a probe of the pore structure. For simple systems, the present technique can give an estimate of ${\mathit{V}}_{\mathit{p}}$/S in the range of 10–1000 μm.

Using high-precision neutron-scattering data, we show that the momentum distribution, n(k), in normal ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ differs significantly from the classical, Maxwell-Boltzmann distribution while n(k) in liquid neon is Maxwellian. Final-state contributions to the scattering function are also determined from the data. In helium these are most conveniently represented as a final-state broadening function and in neon as additive corrections to the impulse approximation.

The angular dependence of the magnetic dichroism in core-level photoemission using linearly polarized light has been measured. The intensity asymmetry of Co 3p spectra of Co/Cu(100) ultrathin films upon magnetization reversal has been determined in normal emission, under variation of both polar and azimuthal angles of light incidence. The results are compared to general theoretical predictions of angle-resolved x-ray magnetic dichroism for photoemission along directions of high symmetry. Good agreement between the experimental results and the predicted angular dependences is found, thus confirming that interference terms in the dipole matrix elements are responsible for the angle-resolved magnetic dichroism.

The self-induced gap soliton theory in monatomic lattices proposed by Kivshar [Phys. Rev. Lett. 70, 3055 (1993)] is generalized to one-dimensional Heisenberg ferromagnets. It is shown that the self-induced magnetic gap solitons may exist due to a nonlinearity-induced gap in the continuum magnon spectrum. The evolution of these localized structures is studied in the phase plane and analytical expressions are obtained.

Solid phase epitaxy was used to grow two-dimensional, ordered alloys of MnCu and MnNi on the surface of Cu(100) and Ni(100) crystals. These surface alloys, which have structures that are not present in the bulk phase diagram, result in highly corrugated surface layers with a c(2×2) periodicity. The large outward relaxation of Mn atoms has been predicted theoretically to be due to magnetism of the Mn atoms. Using a combination of soft-x-ray absorption spectroscopy and x-ray magnetic circular dichroism, we have found an enhanced local magnetic moment and long-range magnetic ordering in these surface alloys. We find that Mn is in a high-spin ground state, which stabilizes the surface reconstruction, but that long-range magnetic ordering is not always present. Compositionally ordered MnNi films, with the same c(2×2) surface periodicity, show ferromagnetic coupling of Mn atoms, unlike the antiferromagnetic ordering found in the bulk alloy.

Elastic neutron-scattering measurements on two samples of Cu alloyed with 1.3% Mn and 0.55% Mn show that the spin-density-wave (SDW) features found in more concentrated alloys persist in the limit of very dilute alloys. These features consist of temperature-dependent incommensurate peaks in magnetic neutron scattering, with positions and strengths which are fully consistent with those in the concentrated alloys. The implications of these measurements are twofold. First, it is clear from our data that SDW magnetic ordering occurs across the entire range of Cu-Mn alloys which have typically been interpreted as spin glasses. Second, the more fundamental significance of this work is the suggestion via extrapolation that a peak in the magnetic susceptibility χ(q) occurs in pure copper, at a value of q given by the Fermi-surface diameter 2${\mathit{k}}_{\mathit{F}}$.

Melt-spun ribbons and thin films of amorphous ${\mathrm{Zr}}_{60}$${\mathrm{Cu}}_{40}$ have been studied. Disorder was varied by neutron irradiation, Xe ion irradiation, and condensation on substrates at different temperatures. A correlation was found between the data for the superconducting ${\mathit{T}}_{\mathit{c}}$, and the residual resistance ratio, described by one curve for all samples. Increased electronic disorder was found to be the cause for this correlated depression of ${\mathit{T}}_{\mathit{c}}$ and increasing residual resistance ratio. These results also give evidence for electronic disorder effects in the electrical resistivity of amorphous ${\mathrm{Zr}}_{60}$${\mathrm{Cu}}_{40}$ up to room temperature.

Several sum rules for x-ray-absorption (XAS) dichroism have been recently derived. Here we discuss the particular case of linear polarization, relevant to cuprate oxides. We apply this analysis to the ${\mathit{L}}_2$ and ${\mathit{L}}_3$ edges of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ in order to obtain quantitative, model-independent information about the out-of-plane character of 3d holes. A Cu 3${\mathit{d}}_{3\mathit{z}}^2$-${\mathit{r}}^2$ to 3${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ ratio of 3% is found for an insulating and two superconducting samples, and of 7% for the overdoped one. The interest of measuring both the ${\mathit{L}}_3$ and ${\mathit{L}}_2$ edges to perform similar XAS sum-rule analysis in higher-${\mathit{T}}_{\mathit{c}}$ cuprates is discussed.

The role of thermal vortices in the absence of applied magnetic fields is studied theoretically for anisotropic layered superconductors such as the high-${\mathit{T}}_{\mathit{c}}$ cuprates. Using a quasi-two-dimensional model and a real-space renormalization-group approach, the vortices are found to Josephson-decouple the superconducting layers slightly above ${\mathit{T}}_{\mathit{c}}$. The results are consistent with recent experiments and Monte Carlo simulations.

The normal-state transport properties are studied in the flux-binding phase of the t-J model within the framework of gauge theory. We find that the resistivity is linearly temperature dependent with a relaxation rate ħ/τ≃2${\mathit{k}}_{\mathit{B}}$T. We also show that the Hall coefficient involves a second relaxation rate and the cotangent Hall angle follows a ${\mathit{T}}^2$ law. Furthermore, the thermopower exhibits a strong-doping dependence. All these features are in good agreement with the transport measurements of the high-${\mathit{T}}_{\mathit{c}}$ copper-oxide compounds.

On the basis of the behavior of the coherence length of disordered cuprate superconductors, it has been found that in these systems there is a direct suppression of the effective pairing interaction between the carrier holes by the doped impurities. A phenomenological model has been set up to examine the effect of the suppression of the pairing interaction on the degradation of the superconducting transition temperature. It is argued that the direct suppression of the pairing interaction is a dominating source of ${\mathit{T}}_{\mathit{c}}$ degradation in the cuprate superconductors.

Understanding the role of pressure in increasing ${\mathit{T}}_{\mathit{c}}$ is a crucial issue in mercury-based superconductors. We report on the effect of pressure on the Raman frequency (ω) of the apical oxygen (${\mathrm{O}}_{\mathit{A}}$) in Hg-${\mathrm{O}}_{\mathit{A}}$-Cu bonds of ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{2\mathit{n}+2+\mathrm{\delta }}$ superconductors. For both Hg-1201 and Hg-1223, Δ(${\mathrm{\omega }}^2$/${\mathrm{\omega }}_0^2$)/ΔP is found to be strongly correlated with Δ${\mathit{T}}_{\mathit{c}}$/ΔP, where ${\mathrm{\omega }}_0$ is the frequency at ambient pressure. Together with our local-density approximation total-energy phonon study of the ${\mathrm{O}}_{\mathit{A}}$-${\mathit{A}}_{1\mathit{g}}$ Raman mode, it is concluded that the change of the ${\mathrm{O}}_{\mathit{A}}$ Raman frequency is due to the change in Hg-${\mathrm{O}}_{\mathit{A}}$ bond strength, which may be directly related to the charge transfer between the ${\mathrm{CuO}}_2$ planes and the Hg-O layers.

Field-effect mobility and conductance of ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ single crystals as functions of temperature are presented. An analysis of the observed high field-effect mobility of ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ (∼2 ${\mathrm{cm}}^2$/V s) indicates that the density of localized states near the surface is much smaller than in films of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathrm{\delta }}$ studied previously.

In a recent paper [Phys. Rev. B 47, 14 233 (1993)], Mandal and Ghatak claimed that a relative change in ac resistance up to 12% by changing the applied field was found in a Co-rich amorphous wire. This large change was ascribed to the giant magnetoresistance effect. We have made both dc and ac four-probe measurements on wires of the same composition under applied fields and no such large change has been observed. We believe that the results commented on reflect the strongly field-dependent self-inductance. Although the reactance at low frequencies is very small compared with the resistance, its effect could be enhanced under some circuit conditions.