Operator regularization in background-field quantization facilitates the use of a perturbative expansion due to Schwinger to compute Green’s functions to all orders. The procedure is distinct from the usual Feynman technique. No explicit divergences are encountered. We illustrate with a ${\phi }_6^3$ theory and discuss applications to QED, supersymmetry, axial models, and quantum gravity.

Evidence is presented for five closely spaced states in ${}_{}{}^{118}{}_{}{}^{}\mathrm{Cd}$ near $E_{\mathrm{ex}\mathrm{\simeq }2}$ MeV, which are interpreted as a near-harmonic three-phonon quintuplet. Candidates for even higher-lying multiphonon states are also found. The experimental spectrum is compared with an anharmonic vibrator [or U(5) spectrum] and an interacting-boson-approximation calculation incorporating a two-particle, four-hole intruder configuration.

We propose the exact values of the tricritical exponents of a collapsing polymer in two dimensions: ν=(4/7, γ=(8/7, and φ=(3/7. They are obtained in a model of self-avoiding walk on a hexagonal lattice, with random forbidden hexagons, whose percolation threshold gives the exact tricritical point. The infinitely many exact tricritical exponents then derived from Coulomb gas methods are critical exponents of the O(n=1) Ising model below ${\mathrm{T}}_{\mathrm{c}}$. The numerical check is very good.

It is predicted that a laser’s phase-diffusion rate (its Schawlow-Townes linewidth) may be reduced by as much as one-half when the laser is coupled out to ‘‘squeezed vacuum’’ as opposed to ordinary vacuum. The effect is important because it is directly related to spontaneous emission in a squeezed vacuum. It shows that a part of spontaneous emission is due to amplified zero-point noise and that, therefore, in a squeezed field the random phases of the spontaneously emitted photons are no longer uniformly distributed.

A gyrotron oscillator with a single cylindrical cavity has produced output powers up to 645 kW and efficiencies up to 24% at 140.8 GHz, and step-tunable single-mode operation between 126 and 243 GHz. Mode stability and suppression of nearby competing modes are found to persist even for operation in very high-order cavity modes with severe mode competition. These results greatly improve prospects of developing cw megawat gyrotrons relevant to the heating of fusion plasmas.

We report the first experimental observation of chaotic behavior and period doubling in a pulsed plasma discharge sensitive to initial and boundary conditions. The Feigenbaum constants have been measured experimentally in one of the observed chaotic discharge routes.

We report measurements of the state of wetting of two liquid mixtures at coexistence near their respective critical consolute temperatures. Borosilicate glass capillary tubes were reacted with hexamethyldisilazane to produce substrates of uniform and controlled silylation. Surfaces of low coverage exhibit a series of first-order partial to complete wetting transitions and obey a short-range force scaling relation. Surfaces of high coverage yield surprising results which may be understood as a consequence of long-range forces.

The angular anisotropies of x-ray photoelectron and Auger peak intensities from Cu in epitaxial Ni-Cu-Ni(100) sandwich structures allow, for the first time, the breakdown of the observed diffraction from a crystal into the contribution from each layer of atoms. These data show that the primary role of multiple scattering of the outgoing electron wave is to deflect electron trajectories, thereby removing intensity from the strong forward-scattered beams which form upon the initial scattering events, i.e., scattering by nearest-neighbor and next-nearest-neighbor lattice atoms.

At fixed temperature the ortho concentration in solid ${\mathrm{T}}_2$, as monitored by NMR, is found to decay exponentially in time with a time constant that has a minimum at 11.4 K. At 11.4 K the ortho to para conversion in ${\mathrm{T}}_2$ is 200 times larger than in ${\mathrm{H}}_2$. This enhanced conversion rate is attributed to diffusing atoms created by the tritium β decay. A hopping model is used to infer the atom number density and hopping frequency as functions of the temperature.

We show that the soft x-ray emission spectrum of the boron K core exciton in ${\mathrm{B}}_2$${\mathrm{O}}_3$ displays the largest phonon coupling effects yet observed in core spectroscopies. We interpret the observed double-peaked spectrum as the first clear example of phonon ringing. It is necessary to modify the existing theory of this effect by including anharmonicity in order to obtain an accurate description of the experimental results.

The temperature of the structural phase transition in GeTe is calculated complete ab initio from a model lattice-dynamical Hamiltonian that is constructed from microscopic quantum-mechanical total-energy calculations. The phase transition in the model system is studied through a renormalization-group-theory approach, leading to the prediction of a fluctuation-driven first-order transition at 657±100 K.

Piezomodulated Raman scattering is used to determine the extent of anharmonicity, the phonon-phonon coupling, and the presence of modes involved in the phase transition of 1,2,4,5-tetrabromobenzene. The experiments support earlier theoretical predictions and demonstrate that piezomodulated Raman spectroscopy is an important new approach to the experimental study of lattice dynamics.

The normalized intensities of the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ NMR spectra in Si:P decrease when the phosphorous content is lowered through the concentration ${\mathrm{n}}_{\mathrm{c}}$ for the metal-insulator transition. The ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ NMR shift is maximum for ≃1.1${\mathrm{n}}_{\mathrm{c}}$ and becomes very small for n≃${\mathrm{n}}_{\mathrm{c}}$. For n≃1.2${\mathrm{n}}_{\mathrm{c}}$ electronic susceptibility χ on the observed nuclei does not follow the T variation of the macroscopic susceptibility but has all the characteristics expected for a Pauli electron gas. Already above ${\mathrm{n}}_{\mathrm{c}}$, disorder and correlations therefore induce spin localization on an inhomogeneous scale in uncompensated semiconductors.

Although Landau quantization is absent in the interior of open-orbit metals, electron orbits near sample edges require quantized areas. The edge orbits have very small effective masses and hence can produce anomalously large oscillations in magnetization and matnetoresistance. The quantized edge states are largely independent of the magnetic-field–induced spin-density-wave transitions which occur in two-dimensional open-orbit metals. We propose that these edge states are responsible for the anomalous Schubnikov–de Haas and de Haas–van Alphen oscillations observed in the organic tetramethyltetraselenafulvalene salts conductors (TMTSF${)}_2$X.

Arguments are given that, for random spin systems, the density of states ρ(μ) of the inverse of the susceptibility matrix vanishes as ρ(μ)∼exp(-A/μ), for μ→0, throughout the ‘‘Griffiths phase.’’ The amplitude A vanishes at the onset of magnetic long-range order, and diverges at the transition between ‘‘Griffiths’’ and ‘‘paramagnetic’’ phases. For an O(m) spin system, with m→∞, the spin autocorrelation function C(t) is found to have the ‘‘stretched-exponential’’ form, lnC(t)∼-(At${)}^{1/2}$, in the Griffiths phase.

A new configuration-coordinate model for EL2, where the excited state has asymmetrical dual minima, is proposed to explain the oscillatory spectrum of transition rate obtained by a novel spectral photocapacitance transient analysis measurement. The model claims that an electron in the excited state of EL2 has a probability of relaxing both to the conduction band and to the metastable state. It can explain a Gaussian shape of the photoquenching spectrum which cannot be interpreted with the conventional scheme. The proposed model suggests that EL2 in GaAs originates from a complex defect of arsenic antisite with arsenic interstitial atom(s).

Partial spin polarization of heavy fermions and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ liquid is shown to suppress well-defined and easily measurable fractions of the nonanalytic contributions to quasiparticle energies and scattering times. $C_v$(T) measurements can then test (a) the strength of low-Q spin-fluctuation contributions to heavy-fermion interactions, and (b) the present theory of nonanalytic energy terms in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.

We report the first observation of the nearly degenerate four-wave–mixing spectrum of ${\mathrm{Nd}}^{3+}$-doped β’’-Na-alumina. In a new application of continuous-wave high-resolution nearly degenerate four-wave mixing, a linewidth analysis of ∼1-kHz-wide optical resonances in heavily doped samples has been used to explain concentration-dependent, nonradiative decay of Nd ions which is obscured in conventional fluorescence-decay studies. Quantitative four-wave–mixing saturation studies also reveal a transition between a ‘‘closed’’ and an ‘‘open’’ quantum system due to pair interactions at a Nd density of ∼6×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$.

We show that dynamical systems with spatial degrees of freedom naturally evolve into a self-organized critical point. Flicker noise, or 1/f noise, can be identified with the dynamics of the critical state. This picture also yields insight into the origin of fractal objects.

We show that when a member of the quark doublet obtains a mass much larger than any other scale, this standard-model doublet becomes a nonlinear realization of SU(2). While the S-matrix elements are SU(2) invariant, the Green’s functions are not. We explicitly display the one-loop effective Lagrangean with external Higgs scalars.