Growth of Mn on GaAs(100) is studied by photoemission and electron-energy-loss spectroscopy. We find that the first layer of Mn grows on GaAs(100) in a two-dimensional mode, where about 10% of the Mn atoms take part in the chemical reaction with the substrate. The electronic structure of the ultrathin film of Mn is found to be very different from that of bulk α-Mn, and the possibility that magnetic ordering exists in the ultrathin overlayer of Mn is proposed.

To gain a starting point for an explanation of a recent experiment by Takeda et al. on ${\mathrm{NaTiO}}_2$, the triangular-lattice antiferromagnetic Heisenberg model with S=1/2 is investigated by a fermion mean-field theory. We find two self-consistent solutions that describe a spin disordered state with a finite excitation gap. Both phases are consistent with the experiment and thereby should be regarded as promising candidates for the physical state realized in ${\mathrm{NaTiO}}_2$.

The transition temperature in the classical two-dimensional isotropic antiferromagnet in a uniform magnetic field, applied perpendicular to the xy plane, is calculated using a self-consistent spin-wave theory. The effect of vortex-antivortex bound pairs to the transition temperature is estimated.

The super-heavy-fermion compound YbBiPt has the largest known linear specific-heat coefficient γ=8 J ${\mathrm{mol}}^{\mathrm{-}1}$ ${\mathrm{K}}^{\mathrm{-}2}$, and the source of this enormous ‘‘electronic’’ specific heat is of great current interest. Here we describe neutron-diffraction studies that indicate its previously reported crystallographic structure to be incorrect. We find that the Pt atom is on the unique site and can be thought of as an interstitial in a fictitious rock-salt structure YbBi, which can in turn be thought of as an ordered form of elemental bismuth. We find no evidence of disorder between sites, occupancy on the nominally vacant site, nor for any tetragonal or rhombohedral distortions or displacements. Furthermore, any ordered magnetic moment at low temperature must be less than 0.25${\mathrm{\mu }}_{\mathit{B}}$. The sample contains 8.1 wt. % elemental Bi, and if this is typical of other samples, the previously published values for molar susceptibilities and specific heats should be scaled up by this amount to obtain the intrinsic properties of YbBiPt alone.

Dichroic interference effects were observed in circularly polarized soft-x-ray reflectivity at the Co ${\mathit{L}}_{2,3}$ edges of a magnetic multilayer. The data show a maximum asymmetry ratio of 80%, greater than the degree of circular polarization of the incident light, a changeover in the dichroic characteristics with increasing grazing angle, and an inverted interference pattern in the angular dependence of the asymmetry ratio. These observations are explained successfully by a classical electromagnetic model calculation which includes the complete polarization state of the incident light and spatial interference within the multilayer.

A first-principles theory of alloy ordering in two and three dimensions in the presence of ferromagnetism is described. Using the generalized perturbation method, the order-disorder transition from the bcc ${\mathrm{Fe}}_{50}$${\mathrm{Co}}_{50}$ random alloy into the ordered CsCl-structure FeCo alloy and its ordering temperature are found to agree reasonably well with available experimental data. A similar ordering tendency for the formation of the ordered c(2×2) phase of the ${\mathrm{Fe}}_{50}$${\mathrm{Co}}_{50}$ surface alloy on fcc Cu(001) is investigated.

At high magnetic field, the semiclassical approximation which underlies the Ginzburg-Landau theory of the mixed state of type-II superconductors breaks down. In a quasi-one-dimensional superconductor with an open Fermi surface, a high magnetic field stabilizes a cascade of superconducting phases which ends in a strong reentrance of the superconducting phase. From a microscopic mean-field model, we determine the thermodynamics and the excitation spectrum of these quantum superconducting phases.

We analyze the longitudinal four-probe conductance of mesoscopic normal and superconducting wires and predict that in the superconducting case, large negative values can arise for both the weakly disordered and localized regimes. This contrasts sharply with the behavior of the longitudinal four-probe conductance of normal wires, which in the localized limit is always exponentially small and positive.

The changes in the hole carrier concentrations in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ are calculated for uniaxial compressions. We find that while a compression along the a axis enhances the hole density, the one along the b axis results in an almost equal decrease. Due to this cancellation, the pressure dependence of ${\mathit{T}}_{\mathit{c}}$ under a hydrostatic pressure is essentially the same as for a uniaxial stress along the c axis. A qualitative discussion is also given of the strikingly different behavior in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ which is attributed to the chain-chain interaction in this compound.

The magnetic-field dependence of the specific-heat measurements on ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{TbCu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ with 0.5 K<T<30 K, are reported in order to study the magnetic order in this compound. Anomalies in the specific heat C(T) of ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{TbCu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ are observed at ${\mathit{T}}_{\mathit{N}1}$∼5.3 K and ${\mathit{T}}_{\mathit{N}2}$∼2.4 K, which are related to two antiferromagnetic transitions in the Tb sublattice. While the anomaly seen in the specific heat as well as in the magnetic susceptibility at ${\mathit{T}}_{\mathit{N}1}$∼5.3 K is suppressed, the peak position is unaffected with increasing magnetic fields. On the other hand, the anomaly at ${\mathit{T}}_{\mathit{N}2}$∼2.4 K is quickly suppressed by a low field. The entropy change associated with the magnetic transitions deduced from the specific heat of ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{TbCu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ by subtracting the data from ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{YCu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ up to T=12 K is about 5.8 J/mol K (∼R ln2), indicative of a doublet ground state for Tb in the crystalline electric fields. In addition, the magnetic specific heat far below the transitions has the form ${\mathit{C}}_{\mathit{M}}$(T)=${\mathit{AT}}^2$+B/${\mathit{T}}^2$, suggesting contributions from two-dimensional magnon and nuclear Schottky, respectively. These results are discussed in comparison to those of related compounds, such as R${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ and ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$R${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$.

The structure of the effective electron-electron interaction in the doped two-dimensional Hubbard model is examined. Monte Carlo results for the irreducible electron-electron vertex in the singlet channel are compared with a spin-fluctuation exchange approximation for the effective interaction. We conclude that the exchange of paramagnetic-antiferromagnetic spin fluctuations mediates the effective-pairing interaction in the weak-to-moderately-coupled Hubbard model.

The London-penetration-depth anisotropy ratio γ of ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$(${\mathrm{Y}}_{0.7}$${\mathrm{Ca}}_{0.3}$)${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ and Ca-free ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{Y}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ (y≊0.1) single crystals has been measured by the equilibrium torque magnetometry method. γ values are found to be in the range of 10 to 11 and are comparable to that of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ rather than ${\mathrm{Bi}}_{2+\mathit{x}}$${\mathrm{Sr}}_2$${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ although ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$(${\mathrm{Y}}_{0.7}$${\mathrm{Ca}}_{0.3}$)${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ is structurally similar to both, with its c-axis lattice constant 30% larger than that of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. The γ of a ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$(${\mathrm{Sm}}_{0.5}$${\mathrm{Eu}}_{0.5}$)${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ crystal was measured to be 13±3.

Thermoelectric transport due to the motion of free unbound vortices above the Kosterlitz-Thouless transition temperature is considered. It is shown that the Magnus force, which appears under the influence of the temperature gradient, leads to a nonzero thermopower at a temperature above the Kosterlitz-Thouless transition temperature ${\mathit{T}}_{\mathrm{KT}}$, but below the mean-field (Ginzburg-Landau) critical temperature ${\mathit{T}}_{\mathrm{GL}}$. The exponential inverse-square-root reduced-temperature dependence of the thermopower above ${\mathit{T}}_{\mathrm{KT}}$ is predicted with a consequent broadening of the superconducting transition detected by means of thermopower measurements. The case of the clean superconductor is analyzed.

A comparative study of the short-range order in mechanically alloyed and melt-spun HfCu alloys has been presented [Phys. Rev. B 47, 7732 (1993)]. We comment on the amorphous nature of some of these samples and on some controversial conclusions in that paper.

We present some noteworthy facts for discussion of the short-range order in the amorphous alloys from the time-differential perturbed-angular-correlation (TDPAC) spectra in reply to the comment of Mendoza-Zélis, Damonte, and López García.

Rates of electron detachment form secondary ${\mathrm{C}}_{60}^{\mathrm{-}}$ ions sputtered by swift atomic projectiles (19.7-MeV S, 48.6-MeV Br, and 78.2-MeV I) from ${\mathrm{C}}_{60}$ films are determined and employed to estimate the internal excitation energy of the sputtered ${\mathrm{C}}_{60}^{\mathrm{-}}$ ions. While the ${\mathrm{C}}_{60}^{\mathrm{-}}$-ion yields vary as the third power of the incident ion energy loss in the solid, no dependence has been found in the internal energy content of sputtered ${\mathrm{C}}_{60}^{\mathrm{-}}$ ions on ion parameters. These results illustrate the use of ${\mathrm{C}}_{60}$ fullerenes as a ‘‘molecular thermometer,’’ and contribute to the elucidation of the ion-sputtering process.

The electrical conductivity and Hall effect of Al-Cu-Ru and Al-Cu-Fe quasicrystals have been studied in the temperature range 4.2–300 K. Through measurements on samples annealed at various temperatures we found that ordering of the quasicrystalline phase has a strong influence on electrical properties. The largest temperature variations of the Hall coefficient were observed in highly ordered Al-Cu-Ru samples, which also show the highest resistivities. The temperature dependence of the Hall coefficient implies that there exists a change in the carrier density. The electrical transport below 30 K is consistent with weak-localization and electron-electron-interaction theories. Conversely, at temperatures above 30 K, the observations can be consistently understood by recognizing that the increase of carrier density with increasing temperature overcomes the decrease of mobility. The characteristics of transport above 30 K are qualitatively similar to those of normal semiconductors.

We derive and analyze the statistics of reflection coefficient of light backscattered coherently from an amplifying and disordered optical medium modeled by a spatially random refractive index having a uniform imaginary part in one dimension. We find enhancement of reflected intensity owing to a synergy between wave confinement by Anderson localization and coherent amplification by the active medium. This is not the same as that due to enhanced optical path lengths expected from photon diffusion in the random active medium. Our study is relevant to the physical realizability of a mirrorless laser by photon confinement due to Anderson localization.

Metastable fcc ${\mathrm{Al}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ solid solutions in the low Si concentration range are modeled by the embedded-atom method. The potential parameters for Si are fitted to the experimental lattice constant of the solutions, the cohesive energy, and the elastic properties of the metallic simple-cubic phase of Si determined by ab initio computations. The model reproduces and explains the concentration dependence of the vibrational density of states, the decrease of the shear modulus with increasing x, and allows us to simulate the first stages of the alloy decomposition into Al and Si.

We study the possibility of kink motion induced by pure ac driving in damped nonlinear lattices, focusing on the Frenkel-Kontorova and Toda models. Numerical simulations of the Frenkel-Kontorova model show no evidence for steady kink motion. We point out that momentum-balance in addition to energy-balance arguments are needed to understand the translation of the collective excitation. Finally, our result is discussed in view of related theoretical predictions and numerical simulations.