We have studied the injection of excess charge into the lightly p-doped compensated GaAs semiconductor layer of a metal-insulator-semiconductor heterostructure. Below a few Kelvin, the length over which excess carriers screen an applied voltage step grows dramatically as the step size is decreased. This nonlinear screening reflects the reduced density of states near the Fermi level caused by electron-electron interactions (the Coulomb gap). The nonlinearities persist for minutes or longer, demonstrating the existence of an electron-glass regime.

Ferromagnetic order in Fe(110) monolayers on W(110) was analyzed with use of conversion electron Mössbauer spectroscopy. The Ag-coated monolayer is ferromagnetic up to ${\mathrm{T}}_{\mathrm{C}}$(1)=296 K=0.28${\mathrm{T}}_{\mathrm{C}}$(∞). The gross shape of ${\mathrm{B}}_{\mathrm{hf}(\mathrm{T}}$) resembles that of bulk material. ${\mathrm{B}}_{\mathrm{hf}(0\mathrm{}}$) is reduced to 11.9±0.3 T. In the critical region 275 K≤T≤295 K, a continuous transition from a magnetic to a nonmagnetic component takes place. For the uncoated monolayer, the ground-state hyperfine field and Curie temperature are reduced to ${\mathrm{B}}_{\mathrm{hf}\mathrm{}\left(0\right)=10\mathrm{}\pm 1}$ T and ${\mathrm{T}}_{\mathrm{C}}$(1)=210 K=0.20${\mathrm{T}}_{\mathrm{C}}$(∞), respectively.

Thin magnesium films in a weak localization regime have been studied at low temperatures in an applied microwave field. The effect of amplitude and frequency of the microwaves has been measured. Measurements of the low-field magnetoresistance as a function of microwave power allow us to conclude that the microwaves give rise to a phase-relaxation rate which is independent of and additive to the intrinsic phase-relaxation mechanisms. Our experiments support the theoretical predictions by Altshuler, Aronov, and Khmelnitsky. The change of the dc resistance of our films with microwave power in zero dc magnetic field has also been measured. We find this to be only partly explained by the phase-relaxation rate deduced from the magnetoresistance.

We report the first contact-free measurements of the upper critical fields, ${\mathrm{H}}_{\mathrm{c}2}$(T), of single-crystal ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$. In contrast to resistive measurements reported by others, we find that the anisotropy near ${\mathrm{T}}_{\mathrm{c}}$ is temperature independent in agreement with the expectations of anisotropic Ginzburg-Landau theory. Estimates of the anisotropic Ginzburg-Landau and London parameters are reported. These indicate that despite the large anisotropy in ${\mathrm{H}}_{\mathrm{c}2}$ (5:1), the inferred low-temperature interplanar coherence length (${\xi }_{\mathrm{z}}$=7 Å) remains larger than the Cu-O layer spacing of 3.9 Å. The superconductivity in ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ thus remains fundamentally three dimensional in nature for a substantial temperature range below ${\mathrm{T}}_{\mathrm{c}}$.

The spatial distribution of adsorbed virus particles on a quartz surface was measured by electron microscopy. For low surface concentrations of adsorbed particles (around ${10}^8$ particles per squared centimeter) the distribution was found to deviate from a random distribution. The particles with a diameter of 54 nm were found to interact at distances up to 0.7 μm. These interactions showed up both in the pair distribution function g(r) and in the nearest-neighbor distance distribution.

We have used quasielastic light scattering to measure the bond orientational elasticity and viscosity of thin tilted hexatic liquid crystal films. Our results agree well with a microscopic model of the dynamics of a hexatic. We have also discovered a novel optical mode corresponding to the out-of-phase motion of the tilt field and bond angle field. This mode softens dramatically at the structural phase transition from hexatic I to hexatic F.

Vortex-free states have been observed in ${}_{}{}^3{}_{}{}^{}\mathit{B}$ at rotation speeds up to 0.9 rad/s in a cylinder of 5-mm diameter. The measured cw NMR spectra, reflecting the order-parameter structure, respond very differently to rotation in opposite directions. The sign of this asymmetry is not linked to the direction of the applied magnetic field, as expected for a gyromagnetic effect, but varies randomly from one cooldown to another.

A 2D quasicrystal with an eightfold rotational axis has been found in rapidly solidified V-Ni-Si and Cr-Ni-Si alloys by means of transmission electron microscopy. The electron diffraction pattern taken along this axis shows no periodicity but a clear eightfold orientation symmetry. The corresponding high-resolution electron microscopic image agrees well with the 2D eightfold quasilattice consisting of squares and 45° rhombi.

A new concept on optical nonlinearity due to virtual transitions in quantum well structure with electric field, named virtual charge-induced optical nonlinearity, is proposed, with a showing of some examples of theoretical result on the nonlinearity. The switching time of the nonlinearity is expected to be extremely short, 100 fs. The nonlinearity seems to be observable and quite useful for the design of an ultrafast optical gate. A possibility of optical bistability without external optical feedback, based on the proposed nonlinearity, is pointed out.

We consider theoretically a semiconductor quantum well subject to an electrostatic field normal to the layer and a strong monochromatic laser field in the transparency region below the absorption edge. We show that ultrashort optical pulses generate ultrashort voltage pulses because the virtual electron-hole population induced by the laser field partially screens the applied static field. We predict that voltages >1 V could be generated in micron-thick multiple quantum well structures by use of low-power short-pulse lasers.

Optical transitions in ultrathin Si-Ge strained superlattices are computed by means of a simple tight-binding model. The use of strain and folding arguments gives a clear understanding of the different origin of the transitions previously observed. The experimental dependence of intensities with the number of layers in the supercell is found to be a consequence of the fact that these superlattices are type II.

By extension of the functional integral treatment of the Kondo lattice model of heavy-fermion metals to real times, a model transport equation is derived. Frequency- and temperature-dependent conductivity are calculated. Results are contrasted with transport properties of heavy-fermion metals.

We report measurements of torque relaxation in a Cu:Mn (5 at. %) spin-glass sample under a variety of experimental protocols, which can give strikingly different decay patterns. We conclude from the data that relaxation in this type of spin-glass is through local reorganizations of groups of spins rather than by cluster inversions, and that the reorganizations of spins which take place upon the application of a magnetic field to a zero-field–cooled sample are closely linked to the reorganizations which lead to relaxation.

Neutron diffraction and diffuse-critical-neutron-scattering experiments in CeAs reveal most unusual critical phenomena. Below ${\mathrm{T}}_{\mathrm{N}}$=8.5±0.1 K long-range antiferromagnetic ordering is realized, but there exist short-range ordered critical spin fluctuations which exhibit a maximum at ${\mathrm{T}}^{\mathrm{*}}$=7.3±0.1 K much below ${\mathrm{T}}_{\mathrm{N}}$. These fluctuations predominantly involve the direction of the spins and drastically depress the development of the single component of the mean staggered moment giving rise to an apparent exponent β>1. .AE

In this paper we find that the stretched-exponential relaxation commonly observed in disordered systems is explained by time-dependent atomic diffusion. The relaxation is observed in the electronic properties of hydrogenated amorphous silicon (a-Si:H), a ‘‘hydrogen glass’’ material, and reflects the equlibration of localized electronic states. The relaxation is attributed to the motion of bonded hydrogen which exhibits dispersive diffusion with a characteristic power-law time dependence. A quantitative relation between the relaxation and the diffusion is established.

Two closely lying (in energy) states of fcc iron grown on copper (100) have been identified by magneto-optic and photoemission experiments. The as-grown state at 460 K exhibits in-plane surface ferromagnetism in magneto-optic measurements. Ferromagnetism parallel to the plane is not observed for the room-temperature state; its absence is supported by a comparison of our calculated and measured work functions and by the photoemission results. LEED shows expanded interplanar spacing at the surface. The temperature behavior and effect of fresh iron deposition indicate that the thermal transition between the two states is first order.

Zero-field spin precession of positive muons has been observed in the antiferromagnetic state of ${\mathrm{La}}_2$${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$. Sharp onsets of the sublattice magnetization are found at temperatures close to those of the susceptibility maxima of different specimens. The long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Néel temperature. Combination of the present results and neutron-scattering studies indicates the ordered moment per Cu atom to be significantly less than 1${\mathrm{\mu }}_{\mathrm{B}}$.

Reasons for disagreement regarding reference states for half-cell potentials are discussed. It is suggested that the electron at rest at ∞ is the best choice, and the only one that agrees with common physics practice. This reference state is the same as that just outside the electrolyte for large electrolytes. Choose this case and most disagreement disappears. It is also suggested that an electron at ∞ is a good thermodynamic state, with entropy zero and a Gibbs free energy. For half-cells with different electrolytes it is necessary to refer all Fermi levels to the same reference state.

We point out that, on very general grounds, experiments with directionally collimated beams (of neutrons or other particles) incident on passive targets cannot distinguish between their coherent wave-packet structure and the incoherent mixing due, for example, to multiple emitters or to interactions with other particles in the source.

This paper considers the three-dimensional inverse scattering problem for the wave equation with variable velocity. A possible solution is presented in terms of equations whose self-consistent solution determines the velocity from scattering data. These self-consistent equations are (1) the wave equation in integral form, (2) a linear integral equation which relates the wave field and scattering data, and (3) a novel formula for the velocity in terms of the wave field.