We report measurements of the intensity of the scattered light and the turbidity of aqueous solutions of the bovine lens protein, ${\gamma }_{\mathrm{II}}$-crystallin, near the critical point for binary liquiid phase separation, in a region of the phase diagram which is metastable with respect to protein-crystal formation. We have determined the magnitudes and critical divergences of the osmotic compressibility, ${\mathrm{\kappa }}_{\mathrm{T}}$, and the static correlation range, ξ. The corresponding critical exponents are γ=1.21±0.05 and ν=0.68±0.1. .AE

The specific magnetic-field-induced birefringence is measured in isotropic suspensions of the rodlike particle tobacco mosaic virus as a function of concentration and added salt. This quantity is proportional to the angular correlations between particles at zero field. In addition, the isotropic-nematic coexistence concentrations are measured as a function of ionic strength. The data compare well with a scaled functional theory assuming decoupling between the angular and spatial degrees of freedom.

We present the first numerical study of spinodal decomposition in polymer mixtures in three dimensions for the Flory–Huggins–de Gennes free energy, numerically integrating the time-evolution equations for the conserved order parameter. We study the time dependence of the domain size as well as the pair correlation function and structure factors for several quench temperatures. The results indicate that the growth law for the characteristic domain size is independent of the final quench temperature in contradiction with the recent experiments on model polymer systems. As well, it is shown that dynamical scaling is valid at sufficiently late times.

We introduce a new method for the calculation of the x-ray bremsstrahlung isochromat spectra. The method is worked out within a real-space multiple-scattering theory and disposes of the conceptual and practical difficulties inherent in the band-structure calculations. Our concept makes possible to calculate spectra in both near and extended energy regions even for systems lacking translational symmetry. The method is illustrated through a calculation of four isochromat spectra of Cu and Pd. For the first time the extended x-ray-isochromat fine structure is calculated.

We have studied solid molecular hydrogen at pressures up to 167 GPa (1.67 Mbar and temperatures from 4.3 to 150 K. We have investigated the phase transition recently observed by Hemley and Mao near 150 GPa and identified as orientational ordering by studying the Raman vibrational and rotational excitations. The pahse line determined for this transition differs significantly from that expected for the extension of the low-pressure orientational ordering. We conclude that this transition is to a new high-pressure molecular phase which only exists at megabar pressures.

We present ultrasonic experiments on the low-temperature tunneling of H and D interstitials in Nb. Strong isotope effects are observed in the sound velocity and the attenuation. From the temperature dependence of these quantities we determine tunneling matrix elements and relaxation rates for both isotopes. We demonstrate that this isotopic behavior is adequately described by present theories on nonadiabatic interaction of tunneling systems with conduction electrons in the weak-coupling regime.

Conditions for laser amorphization of Si were studied as a function of orientation for samples from [110] surface normal through [111] to [001] at 5° intervals. Two regimes of behavior are observed, one within 15° of [111] and a second for the remaining orientations. The transition energy density for amorphous crystal regrowth and the maximum a-Si thickness changes abruptly between regimes. These results are inconsistent with a single-ledge growth model and suggest that two separate interface morphologies or solidification mechanisms are active in the liquid-phase growth of Si.

The surface-state band structure and symmetry properties of the Si(111)-(√3 × √3) R30°-Ag surface have been studied with polarization-dependent, angle-resolved photoemission. In contradiction to the prevailing picture of this surface, we find an intrinsic, dispersive surface-state band in the bulk band gap. The minimum of this band is located 0.1 eV above the valence-band maximum ($E_V$), and the observed partial occupation of the band determines the Fermi-level position (0.2 eV above $E_V$) on this surface.

High-purity MgO exhibits an unexpected giant anomaly of the apparent static dielectric constant and positive surface charge of the order of 5×${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ in the top 15 nm. We postulate that the MgO matrix contains traces of peroxy defects, ${\mathrm{O}}_2^{2\mathrm{-}}$, associated with ${\mathrm{Mg}}^{2+}$ vacancies. Above ≊400400 °C the ${\mathrm{O}}_2^{2\mathrm{-}}$ dissociates to vacancy bound ${\mathrm{O}}^{\mathrm{-}}$ and highly mobile ${\mathrm{O}}^{\mathrm{-}}$ states, which diffuse to the surface, giving rise to a high surface conductivity.

We calculate the direct coupling among long-wavelength photons and single short-wavelength phonons at the surface of semi-infinite polar crystals. This coupling is allowed due to the loss of momentum conservation at interfaces. The ir reflectance shows deviations of order ${10}^{\mathrm{-}4}$ from the Fresnel spectrum, with a rich structure related to the detailed ionic motions in regions of the phonon dispersion relations commonly regarded as inaccessible to light. The reflectance depends on polarization and crystal orientation, suggesting a new ir optical anisotropy spectroscopy which is expected to be surface sensitive.

Ge-Si strained-layer superlattices have been synthesized on (001) Ge with unit-cell periodicity of ten atomic monolayers along the growth direction. Microstructural characterization establishes extended planar superlattice layering. X-ray diffraction is used to measure the superlattice composition. Optical reflectance spectra show new optical transitions at energies theoretically predicted for superlattice-induced direct optical transitions at the center of the Brillouin zone.

We present the first experimental evidence for the spontaneous breaking of cubic symmetry in the band structure of films of ${\mathrm{Ga}}_{0.52}$${\mathrm{In}}_{0.48}$P grown by organometallic vapor-phase epitaxy on (100) GaAs substrates. We show how this effect is related to the spontaneous ordering of the alloy, and its correlation with the anomalous lowering of the band gap observed in these films.

We investigate the quasiparticle band structure and optical properties of a relaxed GaAs(110) surface using a first-principles Green’s-function approach. The local fields and the dynamical correlation are fully incorporated in the evaluation of the electron self-energy operator. The results provide a quantitative interpretation of the photoemission, inverse photoemission, and reflectivity spectra observed for this surface. Implications of our theoretical surface band structure for the current controversy between various experimental results for the position of the empty surface band are discussed.

We directly determine the momentum conservation rules for tunneling processes between two independently contacted two-dimensional-electron-gas systems on GaAs-GaAlAs heterostructures. In transverse magnetic fields, the conservation of the canonical momentum results in a new and giant broadening of the subband resonances. As a consequence, the mean values of the wave functions, even for nonoccupied subbands, can be determined directly.

A quantum mechanical theory is developed for the recently discovered magnetoresistance oscillations in a periodically and weakly modulated two-dimensional electron gas. The bandwidth of the modulation-broadened Landau levels at the Fermi energy oscillates with magnetic field and gives rise to magnetoresistance oscillations parallel (${\rho }_{\mathrm{xx}}$) and perpendicular (${\rho }_{\mathrm{yy}}$) to the modulation. Diffusion current contributions, proportional to the square of the bandwidth, dominate ${\rho }_{\mathrm{xx}}$; collisional ones, which are large for small bandwidths, dominate ${\rho }_{\mathrm{yy}}$. ${\rho }_{\mathrm{yy}}$ and ${\rho }_{\mathrm{xx}}$ oscillate out of phase as observed. New oscillations in the Hall resistance, the cyclotron resonance position, and the linewidth are predicted.

GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum-well wires with lateral dimensions of 70 nm have been prepared by mesa etching of 14-nm-wide quantum-well systems. In photoluminescence excitation two heavy-hole (hh) exciton transitions, ${\mathrm{hh}}_{11}$ and ${\mathrm{hh}}_{12}$, separated by 2.5 meV, were observed. These transitions result from 1D quantum-confined energy states in the narrow wires. The 1D character was reflected in a strong polarization dependence and in a unique magnetic field behavior indicating an enhancement of the excitonic interaction of the 1D ground state by about 15%.

Narrow quantum wires of sufficiently high mobility exhibit an anomalous, low-field magnetoresistance peak at a position scaling as the ratio of the Fermi wave vector to the wire width. We investigate this effect varying temperature, electron density, sample geometry, and method of lateral confinement. The data we obtain are consistent with a classical explanation based upon a diffuse component of electron scattering at the edges of the wire.

Tunneling measurements on 3D amorphous composite indium plus indium-oxide films reveal anomalous features in the normal-state electron density of states $N_n$(E). Above 2 meV, $N_n$(E) increases linearly with ln(E) as expected for 2D films, rather than √E as expected for 3D films. However, the magnitude of the ln(E) term scales with resistivity ${\rho }_{4.2}$, not sheet resistance $R_{\square }$.

Internal magnetic fields in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$ and ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$ have been investigated below 90 mK using muon spin rotation. In ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$ the static internal magnetic field at the muon site due to magnetic ordering remains constant with increasing x up until x=6.30 and then rapidly approaches zero just above x=6.44. In heavily doped samples of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$ (x≥6.54, $T_c$≥52 K) and ${\mathrm{La}}_{2\mathrm{-}\mathrm{y}}$${\mathrm{Sr}}_{\mathrm{y}}$${\mathrm{CuO}}_4$ (y=0.15, $T_c$=37 K) we find little evidence for static or slowly fluctuating electronic moments. These results clearly establish that static magnetic order is destroyed in regions of high carrier concentration.

We describe a new phase in the supersymmetric t-J model on a tripartite lattice where spin and statistics are simultaneously staggered. This phase contains gapless Goldstone fermions and is of relevance to the Emery model of high-$T_c$ superconductors at large doping x∼1. We also argue that triangular layered Mott insulators may turn into superconductors upon being doped.