A Green’s-function technique is used to study the effects of spin-phonon interactions in ${\mathrm{PbHPO}}_4$- and ${\mathrm{PbDPO}}_4$-type ferroelectrics including higher-order anharmonic terms. The renormalized energy and the damping of the spin-waves and the phonons have been evaluated. The anharmonicity effects play an important role in the vicinity of ${\mathit{T}}_{\mathit{c}}$ and above ${\mathit{T}}_{\mathit{c}}$. The transverse dynamic structure factor exhibits three peaks due to the coupling of the transverse soft mode and the acoustic-phonon mode. The width of the central peak is proportional to the phonon damping.

The ground-state phases of a chiral model which describes orientational order of a single stack of planar objects with threefold symmetry subject to a local anisotropy field are examined. The results are used to interpret experimental data on columnar discotic liquid crystals which exhibit triangular arrays of helically ordered molecular stacks.

We have performed simulations of coexisting liquid and solid phases of aluminum as an efficient way of mapping out the coexistence line. This technique is convenient, as it does not require complicated free-energy calculations for the different phases, but simply allows the system to equilibrate to a co-existence point. By altering the simulation volume and/or energy, a new coexistence point is found. The calculated method temperature is lower than previous results for the identical model; we suspect that this difference is due to the difficulty of calculating the free energy of the liquid phase, leading to inaccuracies in the previous work. A thorough examination of several different system sizes, from 1024 to 65 536 particles, indicates that the results are only weakly dependent upon the system size.

The resonant KLL Auger spectra of fluorine have been measured from in situ evaporated films of LiF, NaF, and KF using synchrotron radiation of the MAX I storage ring, Lund, Sweden. The measured Auger electron spectra show strong enhancement at the F 1s absorption edge. New Auger peaks appear at excitation energies below the photoionization threshold. These peaks are shifted to higher kinetic energies in comparison with the normal Auger spectra. They correspond to the excitation of the core excitons followed by the resonant Auger transitions where the excited electron remains as a screening spectator electron during the Auger decay. With the aid of resonant features we have identified the regions of different character inside the comparatively wide absorption peaks. The atomic picture and the comparison with the isoelectronic Ne atom have been applied successfully in the interpretation of the spectra of F.

The glass transition of ${\mathrm{B}}_2$${\mathrm{O}}_3$ is characterized on time scales ranging from about ${10}^3$ to ${10}^6$ s by continuous measurements of the volume expansion upon cooling and heating. The data show a linear relationship between the glass transition temperature and the logarithm of the heating or cooling rate. The hysteresis of the volume at the glass transition becomes narrower at lower rates. The data are compared to two models for the nonequilibrium kinetics at the glass transition.

Electrical properties of different compositions of lead vanadate glasses are reported in the temperature range 80–500 K. The experimental results are analyzed with reference to theoretical models existing in the literature. It has been observed that at high temperatures, Mott’s model of phonon-assisted small polaron hopping between nearest neighbors is consistent with the data, while at low temperatures the variable-range-hopping model is valid. The hopping at high temperatures in the lead vanadate glasses occurs by the nonadiabatic process in contrast to the vanadate glasses formed with conventional network formers. The hopping model of Schnakenberg can predict the temperature dependence of the conductivity data. The percolation model of Triberis and Friedman applied to the small-polaron-hopping regime is also consistent with the data. The consistency of the low-temperature data with the predictions of the different models cannot be distinguished. The various model parameters such as localization length, density of states, etc., obtained from the best fits are found to be consistent with the glass compositions.

A systematic analysis of large-scale fluctuations in the low-temperature pinned phase of a directed polymer in a random potential is described. These fluctuations come from rare regions with nearly degenerate ‘‘ground states.’’ The probability distribution of their sizes is found to have a power-law tail. The rare regions in the tail dominate much of the physics. The analysis presented here takes advantage of the mapping to the noisy Burgers’ equation. It complements a phenomenological description of glassy phases based on a scaling picture of droplet excitations and a recent variational approach with ‘‘broken replica symmetry.’’ It is argued that the power-law distribution of large thermally active excitations is a consequence of the continuous statistical ‘‘tilt’’ symmetry of the directed polymer, the breaking of which gives rise to the large active excitations in a manner analogous to the appearance of Goldstone modes in pure systems with a broken continuous symmetry.

By use of a modified version of Naarmann’s method, we have synthesized polyacetylene (CH${)}_{\mathit{x}}$. The doping was carried out in liquid phases of iodine and iron chloride, and the samples obtained were [CH(${\mathrm{I}}_3$${)}_{\mathit{y}}$${]}_{\mathit{x}}$ and [CH(${\mathrm{FeCl}}_4$${)}_{\mathit{y}}$${]}_{\mathit{x}}$, respectively. The dopant concentration y is between 0.01 and 0.05, and belongs to the intermediate doping region. The temperature dependence of the dc conductivity for the different dopant concentrations is measured. In doped trans-polyacetylene, charged and neutral soliton pairs are produced in the chains. The conduction mechanism, which is based on the intersoliton hopping of electrons, is the same for polyacetylene with intermediate or light doping. For this reason, Kivelson’s model of the average hopping rate, the Hamiltonian of trans-polyacetylene explored by Su, Schrieffer, and Heeger, and the method of Ambegaokar, Halperin, and Langer, which is related to the average transition rate, are used and the relation between the average hopping rate and the transition rate obtained. Finally, in the light of percolation theory and the variable-range-hopping model, the formula for conductivity is derived. The theory is in good agreement with the experiments.

The optical properties of pure liquid and solid zirconium were investigated in the energy range 1.2–3.5 eV. Zirconium specimens were electromagnetically levitated and melted (melting point 2125 K), and purified of residual oxide and nitride contaminants by heating to temperatures above 2400 K. An automated dual-detector rotating analyzer ellipsometer with a pulsed dye laser light source was employed to measure the optical properties. Measurements were obtained over the full energy range at ca. 2335 K and for selected wavelengths at temperatures from 1850–2600 K, including measurements on the undercooled liquid. Liquid zirconium exhibited sharp peaks in the optical conductivity at 1.39 and 1.55 eV, with 0.1 eV half-widths. Broader maxima occurred at approximately 2.1 and 2.9 eV and appeared to contain additional unresolved structure. Measurements on retrieved solid specimens showed some agreement with prior results on zirconium. Liquid zirconium exhibits greater structure in its optical property dependence on wavelength than does the polycrystalline solid and some similarity to the results of theoretical calculations for single-crystal zirconium.

We present results of the Hall effect measurements in CaAl(Au) amorphous alloys. The Hall coefficients have been found to be negative and independent of temperature. Their magnitudes deviate significantly from the nearly-free-electron calculations, and are reduced by gold doping. These deviations have been accounted for from considerations of the unusual electronic structure of CaAl, and the effects of both s-d hybridization and side-jump mechanism on the conduction electrons.

Small-angle x-ray scattering and x-ray-absorption near-edge spectroscopy (XANES) experiments have been performed on amorphous ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Ge}}_{100\mathrm{-}\mathit{x}}$ alloys over the composition range 0≤x≤72. The observed small-angle x-ray-scattering patterns were compared both with those calculated for a model assuming segregation of the alloys into particular phases and with scattering patterns calculated for voids in a homogeneous matrix. The x-ray-absorption near-edge-structure data were used to test for phase separation. No large-scale phase separation is observed in the semiconductor-metal transition region (15–25 at. % Fe), but fine-scale, kinetically limited phase separation or other types of composition fluctuations cannot be ruled out. The results also indicate that phase separation occurs for alloys with 37≤x≤72, with data consistent with separation into amorphous ${\mathrm{FeGe}}_2$ and ${\mathrm{Fe}}_3$Ge. Thus, ferromagnetic moment formation occurs in the phase-separated region, with the transition composition (40–43 at. % Fe) probably linked to a-${\mathrm{Fe}}_3$Ge percolation, as hypothesized by Janot for the related ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Sn}}_{100\mathrm{-}\mathit{x}}$ system. This phase separation explains the Mossbauer observation of ‘‘magnetic’’ and ‘‘nonmagnetic’’ Fe atoms in these alloys.

In situ Doppler-broadening temperature scans and room-temperature positron-lifetime measurements are reported for ${\mathrm{Al}}_{63}$${\mathrm{Cu}}_{25}$${\mathrm{Fe}}_{12}$, ${\mathrm{Al}}_{62.5}$${\mathrm{Cu}}_{25}$${\mathrm{Fe}}_{12.5}$, ${\mathrm{Al}}_{62}$${\mathrm{Cu}}_{25.5}$${\mathrm{Fe}}_{12.5}$, and ${\mathrm{Al}}_{62}$${\mathrm{Cu}}_{22.8}$${\mathrm{Fe}}_{15.2}$ face-centered-icosahedral (FCI) quasicrystalline samples. Quenched-in disorder has been observed and found to anneal out of the samples above 200 °C. A quasicrystal-to-microcrystal phase transition has been observed in two of the samples (${\mathrm{Al}}_{63}$${\mathrm{Cu}}_{25}$${\mathrm{Fe}}_{12}$ and ${\mathrm{Al}}_{62}$${\mathrm{Cu}}_{22.8}$${\mathrm{Fe}}_{15.2}$), indicating an instability of the FCI phase at low temperatures. No such transition is observed in the other two samples (${\mathrm{Al}}_{62.5}$${\mathrm{Cu}}_{25}$${\mathrm{Fe}}_{12.5}$ and ${\mathrm{Al}}_{62}$${\mathrm{Cu}}_{25.5}$${\mathrm{Fe}}_{12.5}$). It is shown that intrinsic structural vacancies, possessing only Al-atom nearest neighbors exist in both the microcrystal and FCI phases and act as saturation traps for the positrons. At ∼200 °C, thermal activation of dynamic Al-atom phasons in the FCI phase results in distortions of the intrinsic structural vacancies as the nearest neighbor Al atoms begin to hop within double-well potentials. At higher temperatures (525–750 °C depending upon the sample stoichiometry) dynamic Cu-atom phasons are activated and observed to coincide with the onset of plasticity in the FCI phase.

It is known that off-diagonal disorder results in anomalous localization at the band center, whereas diagonal disorder does not. We show that the important distinction is not between diagonal and off-diagonal disorder, but between bipartite and nonbipartite lattices. We prove that bipartite lattices in any dimension (and some generalizations that are not bipartite) have zero energy (i.e., band-center) eigenfunctions that vanish on one sublattice. We show that ln‖${\mathrm{\psi }}_{\mathit{j}}$‖ has random-walk behavior for one-dimensional systems with first-, or first- and third-neighbor random hopping, leading to exp(-λ √r) localization of the zero-energy eigenfunction. Addition of diagonal disorder leads to a biased random walk. First- and second-neighbor random hopping with no diagonal disorder leads to ordinary exponential [exp(-λr)] localization. Numerical simulations show anomalous localization in dimensions 1 and 2, with additional periodic structure in some cases.

Using eV neutron scattering, direct measurements have been made of the average single-particle kinetic energies, 〈${\mathit{E}}_{\mathit{k}}$〉, for a series of condensed Ar samples over the range 18–85 K. These temperature-dependent measurements are on a system with A>22 amu in the regime below equipartition. The scattering from liquid-Ar samples, for which it is assumed that 〈${\mathit{E}}_{\mathit{k}}$〉 can be determined with sufficient accuracy from a quantum expansion, has been used to provide information about the total corrections to be made to account for neutron time-of-flight spectrometer resolution and multiple scattering. Data were obtained for wave-vector transfers in the range 192–254 ${\mathrm{nm}}^{\mathrm{-}1}$, to check for possible systematic contributions to experimental uncertainty. The directly measured 〈${\mathit{E}}_{\mathit{k}}$(T)〉 is compared to expectations from thermodynamic experiments, from previous neutron-scattering measurements of collective vibrational modes of the solid, and from various theoretical models. The directly measured temperature dependence provides evidence for use in the interpretation of other experiments which use Ar as an ‘‘inert’’ host.

The electron-phonon relaxation process in niobium has been measured with pump-probe technique and compared with theory for ambient (initial) temperatures ranging from 292 to 7 K. The time it takes for the electrons to thermalize with phonons was found to decrease from 370 fs at 292 K to 250 fs at 7 K, while the electron-phonon coupling parameter g decreases with decreasing temperature.

Polarization-resolved second-order Raman spectra of type-IIa natural diamond for the temperature range 300–1900 K are presented. They are compared with similar measurements made on chemical-vapor-deposition-produced diamond. The high-temperature behavior of the measured critical points for this synthetic diamond sample is very similar to that of the natural diamond sample. Most of the observed optical phonons are found to have a thermal and self-energy shift comparable to that of the longitudinal-transverse-optical (LTO) mode in diamond.

Monte Carlo simulations on self-avoiding walks traced on the simple cubic lattice and reported in a recent paper have been extended up to 2999 steps, using the same Alexandrowicz dimerization procedure. Through this extension, we are able to show that the discrepancy between ${\nu }_{\mathrm{RG}}$, the scaling exponent for the correlation length, as determined from renormalization-group calculations, and ${\nu }_{\mathrm{MC}}$, the same exponent determined through Monte Carlo simulations, is an artefact, originating in the fact that Monte Carlo simulations are restricted to relatively short chains, while to obtain the correct ν value using the latter method exceedingly large chains are required. This finding is in accord with a previous suggestion by Zifferer. We further show that 〈r〉, the modulus of the mean end-to-end distance, 〈${\mathit{r}}^2$${\mathrm{〉}}^{1/2}$, the root-mean-square end-to-end distance, 〈${\mathit{r}}_{\mathit{g}}$〉, the mean radius of gyration, and 〈${\mathit{r}}_{\mathit{g}}^2$${\mathrm{〉}}^{1/2}$, the root-mean-square radius of gyration, cannot be correctly expressed for all N in the range 1<N<2999 using a single correction to scaling exponent ${\mathrm{\Delta }}_1$. At least two such corrections to the scaling exponents are required, and the agreement with the Monte Carlo data is significantly improved if three corrections to the scaling exponents are introduced, so that one should write 〈x〉=${\mathit{N}}^{0.588}$[${\mathit{a}}_0^{\mathit{x}}$+${\mathit{a}}_1^{\mathit{x}}$${\mathit{N}}_1^{\mathrm{-}\mathrm{\Delta }}$ +${\mathit{a}}_2^{\mathit{x}}$${\mathit{N}}_2^{\mathrm{-}\mathrm{\Delta }}$+${\mathit{a}}_3^{\mathit{x}}$${\mathit{N}}_3^{\mathrm{-}\mathrm{\Delta }}$], where 〈x〉 stands for one of the above mean values.

Consideration of a fourth correction to scaling exponent ${\mathrm{\Delta }}_4$ does not seem to be warranted for self-avoiding walks, where there is a lower cutoff for N=1. Further, such a fourth exponent seems devoid of physical significance because of the even-odd oscillations occurring for the lowest N values in the various mean values 〈x〉, where a fourth exponent has a non-negligible effect. A five-term expansion is however given here for completeness. The set of the corrections to the scaling exponents ${\mathrm{\Delta }}_{\mathit{i}}$, which, because of universality, is the same for the various mean values, as well as of the ${\mathit{a}}_{\mathit{i}}^{\mathit{x}}$’s, which depend on the mean value considered, follows the somewhat arbitrary choice made, within a narrow range of values, for the first correction to the scaling exponent ${\mathrm{\Delta }}_1$. If the value ${\mathrm{\Delta }}_1$=0.50 is adopted, as suggested by graphical analysis of our data, the set which minimizes the mean-square deviation of the Monte Carlo data is ${\mathrm{\Delta }}_2$=1.0, ${\mathrm{\Delta }}_3$=2.0, and ${\mathrm{\Delta }}_4$=4.0. If the renormalization group value ${\mathrm{\Delta }}_1$=0.47 is used instead, the corresponding set is ${\mathrm{\Delta }}_2$=1.05±0.02, ${\mathrm{\Delta }}_3$=2.2±0.2, and ${\mathrm{\Delta }}_4$=4.4±0.4. These two sets are mathematically equivalent for the correct description of our Monte Carlo data. The precision of our data does not permit one to decide which set, on a physical basis, is the correct one. In any case, each successive correction to the scaling exponent is found to be, approximately if not exactly, the double of the preceding one.

Using the plane-wave-based linear response method recently developed, the interatomic-force-constant tensor for the noble metal Au is obtained. Using an optimized pseudopotential to model the ion-electron interaction requires only a modest number of plane waves, and the calculated phonon dispersion curves are in excellent agreement with experiment. The force-constant tensor is studied in detail and is compared with those obtained from Born–Von Karman fits to the experimental data. Excellent agreement with experiment is found when the range of interaction is taken to fourth neighbors, however, longer-ranged interactions need to be included to accurately determine the lattice specific heat.

We have measured magnetic circular x-ray dichroism (MCXD) in a remanently magnetized Ni(110) single crystal, with the light in grazing incidence. Measuring the x-ray absorption as a function of the applied magnetic field, we could draw a hysteresis curve similar to one obtained with a magneto-optical Kerr effect on the same crystal. Spectra taken with linearly polarized light show clear variations as the angle of incidence of the light on the sample is changed. The possible origins for this angular-dependent absorption and its consequences for MCXD measurements taken in grazing incidence are discussed.

A general method is proposed for computing the susceptibility of a large category of regular magnetic double chains in which more or less complex quantum spin systems, occupying the uprights and the bunches, are linked through the nodes by magnetic cations. Only two conditions are required: (i) the magnetic cations at the intersections of the uprights and the bunches must exhibit large enough spin quantum numbers to allow a classical treatment and (ii) the overall zero-field Hamiltonian must be isotropic. The main applications of the model are listed. More specifically, results are given for the case where the quantum spin systems are empty, and the neighboring classical spins directly interact through Heisenberg exchange. The model is also used with particular success to interpret the observed magnetic properties of the compound ${\mathrm{Gd}}_2$(ox)[Cu(pba)${]}_3$[Cu(${\mathrm{H}}_2$O${)}_5$]⋅${20\mathrm{H}}_2$O, which enters the general framework, with each quantum system reducing to a single 1/2 spin. It is also applied tentatively to the related compound ${\mathrm{Gd}}_2$[Cu(pba)${]}_3$⋅${23\mathrm{H}}_2$O.