A stochastic density-matrix equation for an atom strongly driven by finite-bandwidth squeezed light is derived. The quantum properties of the light are accounted for by a doubling of dimensions of the stochastic process for $c$-number electric field amplitudes. The possibility of obtaining reduced atomic linewidths in the absorption spectrum of the atom embedded in colored squeezed light is discussed, based on nonperturbative solutions of stochastic optical Bloch equations.

The correction terms to the Sokolov-Ternov radiation formula due to variation of the magnetic field strength along the electron trajectory are calculated up to the second order in the power expansion of $\frac{B_{\tau }}{B}$, where $\tau$ is the formation time of radiation. It is found that the field-gradient effect reduces radiation intensity in the classical regime, and enhances it in the quantum regime. This is then applied to quantum beamstrahlung with Gaussian variation in $e^{+}{e}^{-}$ bunch currents. The correction is shown to be substantial for beam parameters suggested by Himel and Siegrest.

The unsaturated linear rise of the energy confinement time with density, ${\tau }_E\sim {\overline{n}}_e$, up to the density limit is recovered in Ohmically heated discharges in ASDEX. Improvement of a factor of 2 is reached with ${\tau }_E\approx 150$ ms at ${\overline{n}}_e=5\mathrm{}\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$ The improved state is characterized by peaked density profiles. The ion heat diffusivity decreases to the neoclassical value. The parameter ${\eta }_i=\frac{L_{n_e}}{L_{T_i}}$ governing the onset of ion-temperature-gradient modes, falls to the stability threshold. The improvement in confinement might therefore be attributed to the stabilization of ${\eta }_i$ modes.

We demonstrate the relation $\theta =2\mathrm{}\phi$. Here the exponent $\theta$ is defined as $D\sim N^{\theta }$, where $D$ is the equilibrium lamellar thickness of the diblock copolymer ordered phase and $N$ is the molecular weight. The exponent $\phi$ is defined as $l\sim t^{\phi }$, where $l$ is the pattern size of the spinodally decomposing system (say, a binary alloy) and $t$ is the time.

As the Cs coverage of Ag{111} is increased from approximately 0.15 to 0.3 monolayer the Cs-Ag bond length is found to increase from 3.20 ± 0.03 to 3.50 ± 0.03 Å. This dramatic change is associated with a transition in the cesium bonding from predominantly ionic at low coverage towards a more covalent state at high coverage.

A 1D quasicrystal derived from the 2D decagonal quasicrystal has been found in rapidly solidified ${\mathrm{Al}}_{80}$${\mathrm{Ni}}_{14}$${\mathrm{Si}}_6$, ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Mn}}_{15}$, and ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Co}}_{15}$ alloys. They inherit periodicity along the tenfold axis and have, in addition, translation periodicity in one of the twofold axes of the decagonal phase. Crystalline phases based on ordering of vacancies in (111) layers of the CsCl-type structure with a layer sequence of 5, 8, 13, and 21, respectively, have also been found. The important role played by the Fibonacci sequence in these aperiodic and periodic structures is discussed.

By use of the Keldysh nonequilibrium Green's-function methods, analytic expressions are computed for the nonlinear optical susceptibilities for the one-dimensional semiconductor model of a conducting polymer. The model has no adjustable parameter. The results for third-harmonic generation are in excellent agreement with experiments on polyacetylene. Further nonlinear optical effects, which should be experimentally observable, are predicted. The physical significance of these results is discussed.

We have investigated conduction across electron density discontinuities induced by a front gate on $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}}$ single-interface heterostructures in the integral quantized Hall regime. When the gate is biased so that the Fermi level must cross between adjacent Landau levels at the gate edge, the boundary between higher- and lower-density regions behaves like a backward diode, suggesting the presence in these devices of inter-Landau-level tunneling.

Samples of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_{4-\delta }$ have previously shown a maximum concentration of $p=0.15\mathrm{}$ holes per [Cu${\mathrm{O}}_2$] unit, because increasing $x>\mathrm{}0.15\mathrm{}$ normally induces compensating oxygen vacancies. Annealing samples in 100 bars of oxygen pressure fills the oxygen vacancies and greatly increases the range of accessible hole concentrations, up to $p=0.40\mathrm{}$ (or effectively ${\mathrm{Cu}}^{+2.40\mathrm{}}$). We find that $T_c$ is constant at ≃36 K from $p=0.15\mathrm{} \mathrm{to} 0.24$, where it begins to decrease. Beyond $p\simeq 0.32$, superconductivity disappears, even though the samples are more conducting.

The relaxation of microemulsions has been studied by means of the pressure-jump relaxation technique with conductimetric detection. Kohlrausch-Williams-Watts stretched exponentials {$\phi \mathrm{}\left(t\right)=A\exp [-{\left(\frac{t}{\tau }\right)}^b]$} were obtained in which the parameter $b$ increases with temperature from the percolation point of the microemulsions, attaining values greater than 1. These findings entail the existence of spatial, temporal, and energetic disorder associated with temperature-dependent anomalous (inhibited and enhanced) diffusion.

The consequences of the scaling hypothesis in phase-ordering dynamics are examined. Dynamics governed by the time-dependent Ginzburg-Landau and Cahn-Hilliard-Cook equations are studied. An upper bound is found for the dynamical exponents. It is also found that for a critical quench with Cahn-Hilliard-Cook dynamics, if the length scale of the patterns increases as $t^{\frac{1}{3}}$ and the form factor behaves as $k^{\delta }$ for small $k$ then $\delta$ must be ≥ 4. Experimental and numerical results give $\delta \simeq 4$.

We discuss the effect of edge states on the de Haas-van Alphen oscillations in a small singly connected sample made of a 2D electron gas in the quantum-Hall-effect regime. We find that because of the "ring topology" of these states the magnetization oscillates with a period $\frac{\mathrm{hc}}{e}$ in the total flux through the system. This oscillation survives a substantial amount of disorder. Its detectability is discussed and a related oscillation in the longitudinal and transverse resistances suggested.

We show that pairs of simple energy bands exist that have identical symmetries for their Bloch functions, but different symmetries for the corresponding Wannier functions. For finite crystals such pairs of bands belong to equivalent band representations. In the case of infinite crystals, we use the analyticity of simple bands to prove the inequivalence of their band representations. This means that the energies of such pairs of bands cannot coincide despite the identical symmetries of their Bloch functions.

The influence of sliding charge-density waves on the elastic properties of quasi-one-dimensional conductors is investigated. By use of an extension of the Fukuyama-Lee-Rice model the imaginary part of the self-energy of acoustic phonons is shown to diverge in lowest-order perturbation theory above the threshold field. With the summation of leading divergent contributions, the resulting expressions account well for the observed field dependence of the elastic modulus and the ultrasonic attenuation $\alpha$. In particular, a ${\omega }^{\frac{3}{2}}$, instead of the usual ${\omega }^2$, law is predicted for $\alpha$ above the threshold field.

Direct observations of the magnetization structure in two reentrant spin-glass alloys [polycrystalline ${\mathrm{Ni}}_{1-x}{\mathrm{Mn}}_x$ and amorphous ${\left({\mathrm{Fe}}_{78}{\mathrm{Mn}}_{22}\right)}_{75}$${\mathrm{P}}_{16}$${\mathrm{B}}_6$${\mathrm{Al}}_3$] near liquid-helium temperature are reported. Magnetic domains several hundred μm long are seen. This structure hardly changes upon cooling through the reentrant transition ($T_f\simeq 35$ K). In situ observation of the domain-wall motions reveals a gradual crossover to a regime of strong irreversibilities. Reentrant spin-glass systems are also characterized by transverse fluctuations within the domain.

Four different antiferromagnetic arrangements of nuclear spins have been identified in Cu from a Monte Carlo study for different magnetic fields and temperatures. The long-range-dipolar and indirect-exchange interactions were included up to eighth nearest neighbors (140 nuclear spins) and the indirect interaction was calculated from a realistic energy band structure. The phases appear to be compatible with the three phases found in Cu experimentally, and the transition temperature in zero field of about 50 nK is in approximate agreement with the experimental value of 60 nK.

The first Na $K$-edge absorption measurements are reported. The data reveal a narrowing of the unfilled density of states analogous to that observed in a recent photoemission study of the conduction band and in very good agreement with new band-structure calculations. The narrowing is found to be essential for obtaining compatibility among the $K$-edge threshold exponent, the $L_{2,3}$-edge exponent, and the singularity index in core-level photoemission.

We look for possible topological terms in a mean-field Lagrangian for ferromagnets and antiferromagnets inspired by the Hubbard model and study their physical effects. A topological term corresponding to Berry's phase causes the order parameter to behave like a spin moment. We find that the Hopf term is not induced and thus there is no evidence for a neutral fermion in this theory.

It is shown that the O(3) nonlinear $\sigma$ model derived from the quantum Heisenberg antiferromagnet in two spatial dimensions, under the assumption that the Néel field $\hat{\Omega }(\mathbf{r},t)$ is well defined at all points in (2+1)D space-time, has no Hopf term, in contradiction to recent speculation. However, the amplitudes for tunneling between configurations with different spatial topologies reveal a difference between integer and half-integer, and between even- and odd-integer, spins.

Suspensions in a liquid of "nearly hard" colloidal spheres were subjected to steady and oscillatory shear flows and studied by light scattering. Samples which exhibit a fluidlike ordering of the particles in equilibrium were induced to a solidlike order by oscillatory shear of strain amplitude ≃1. In steady shear flow the suspensions showed evidence of "string" structures similar to but less complete than those found in computer simulations of simple liquids.