A high-resolution experiment is reported for spin-wave dynamics in an yttrium iron garnet sphere. For certain parameter values we observe a series of closely spaced spin-wave modes. Interactions between excited modes lead to various dynamical phenomena including auto-oscillations, period-doubling cascades, quasiperiodicity, and chaos. Also observed are irregular relaxation oscillations, abrupt transitions to wide-band turbulence, and hysteresis at the Suhl threshold. A theoretical model is studied analytically and numerically, explaining a number of the experimental behavior patterns.

We have measured magnetoresistance, Hall resistance, and magnetization of tetramethyltetraselenafulvalenium perchlorate [(TMTSF${)}_2$${\mathrm{ClO}}_4$] at low temperatures in fields up to 31 T. Above the cascade of field-induced spin-density-wave transitions, the system remains in a remarkably stable semimetallic state, with constant Landau filling factor (ν), from 8 to 27 T. The measurements indicate that this state is related to the ν=(1/3 fractional quantum Hall effect. At 27 T there is a new transition, to a novel state, distinct in its behavior from the lower-field transitions.

Thin-film, bimetallic systems have been systematically investigated for the first time by means of reemitted-positron energy spectroscopy. Positron work functions for each layer, mean free paths, and thermalization rates can be directly observed. Interdiffusion alloying of a Cu film on Ni is observed. The technique, which is not affected by surface contamination, is highly sensitive as a materials probe of processes that affect the bulk chemical-potential-energy sum, ${\mathrm{\mu }}^{+}$+${\mathrm{\mu }}^{\mathrm{-}}$.

By treatment of the incident and detected electron states in a LEED formalism, it is shown that the dominant processes contributing to a surface electron-energy-loss fine-structure (SEELFS) spectrum from atomic adsorbates on crystal surfaces are those involving elastic backscattering and small-angle inelastic scattering. This justifies the use of the ‘‘dipole approximation’’ for the atomic matrix elements in the interpretation of SEELFS. The angular dependence of the detected electrons is calculated for the first time and its potential for surface structure determination discussed.

A high-precision measurement of the 2$s_{1/2}$-2$p_{1/2}$ Lamb shift in ${\mathrm{He}}^{+}$ is obtained by means of the quenching anisotropy method. The measured value of 14 042.22±0.35 MHz is in excellent agreement with Mohr’s electron self-energy calculation, but disagrees with Erickson’s by more than 8 standard deviations. The accuracy of the measurement provides the most stringent available test of the order-α(Zα${)}^6$${\mathrm{mc}}^2$ contribution to the calculated electron self-energy.

Cross sections for the dissociative recombination of electrons and ${\mathrm{H}}_2^{+}$ ions having low internal energies have been measured by means of the merged electron-ion beam technique. Narrow resonances associated with indirect capture into high-lying Rydberg states of the neutral molecule have been found. The use of ions with only two vibrational states significantly populated has allowed the high-resolution capability of the merged-beam technique to be clearly demonstrated.

Polarization of Cl Kβ x-ray fluorescence following selective excitation of gaseous ${\mathrm{CH}}_3$CL with synchrotron radiation is reported. The degree of polarization of the fluorescence depends sensitively on the chosen incident excitation energy in the Cl K-edge region. Theoretical considerations indicate that the fluorescence-polarization measurements can provide directly absorption and emission anisotropies, molecular-orbital symmetries, and relative fluorescence transition strengths.

In many high-precison laser measurements spontaneous-emission quantum noise determines the ultimate sensitivity. We demonstrate here that when the experimental circumstances restrict us to short measurement times, the spontaneous-emission noise can be substantially reduced by the utilization of long-lived atoms as the masing medium.

We report a sequence of experiments in which 3-μm-thick CH foils were irradiated by one arm of the Nova laser with square pulses of 0.35-μm light. The laser intensity, pulse duration, and spot size were varied to produce plasmas in which the dependence of stimulated Raman scattering (SRS) on laser intensity and on density-gradient scale length could be independently evaluated. The traditional, convective-amplifier model of SRS fails, by many orders of magnitude, to explain either the magnitude or the scaling of these data. We suggest that SRS is absolutely unstable in these plasmas.

Experimental observation of a shock wave generated by soft-x-ray–driven ablation is reported. An aluminum foil was irradiated by soft x rays emitted from a gold plasma. At the soft x-ray intensity of 1.9×${10}^{12}$ C/${\mathrm{cm}}^2$, the shock velocity is measured to be 1.1×${10}^6$ cm/sec. The ablation pressure driving the shock wave is estimated to be 1.3 Mbar. This ablation pressure is in good agreement with the value determined independently from x-ray burn-through measurement.

Nonlinear interactions between flute-type turbulence and an externally excited convective cell in a strongly magnetized plasma are investigated. During the interaction the azimuthal-mode-number spectrum of the turbulence is deformed and a broad spectrum evolves, indicating an inverse cascade. As a result of a modification in phase and amplitude of the fluctuations, an organized structure is created in turbulence. The macroscopic behavior is well explained by a Van der Pol–type equation.

We demonstrate that a plasma can be used as an effective nonlinear medium in a phase-conjugate reflector for subcentimeter electromagnetic waves. The method of production of the amplified phase-conjugate waves is almost-degenerate four-wave mixing. By excitation of collective modes in resonance with the incoming waves the amplification is enhanced significantly.

Electron cyclotron current drive (ECCD) at the second harmonic (ω=2${\Omega }_e$) is demonstrated for two types of plasma in the WT-3 tokamak. When microwave power $P_{\mathrm{EC}}$ is injected into a plasma after Ohmic heating (OH) power is shut down, the plasma current is sustained and ramped up by the EC wave only. Here 2${\Omega }_e$ EC-driven current is generated by 2${\Omega }_e$ EC heating of an energetic electron tail existing in the OH plasma. Further, when $P_{\mathrm{EC}}$ is injected into a microwave discharge plasma, 2${\Omega }_e$ EC-driven plasma current is started up and 2${\Omega }_3$ ECCD plasma is formed without OH power. The 2${\Omega }_e$ ECCD efficiency is the same order as that at ω=${\Omega }_e$, but the 3${\Omega }_e$ EC-driven current is not generated, in contrast with the theoretical prediction.

A temperature-dependent soft-mode behavior is found in the surface–Rayleigh-phonon dispersion curve of 2H-${\mathrm{TaSe}}_2$ by means of inelastic He-atom scattering. The deepest anomaly occurs about 10% below the charge-density-wave onset temperature ${\mathrm{T}}_{\mathrm{o}}$=123 K and is surprisingly located at one-half of the reduced Brillouin zone, unlike the bulk longitudinal-acoustic anomaly which occurs at two-thirds of the zone.

We present neutron-spin-echo results on the dynamics of crosslinks in a tetrafunctional model network of polydimethylsiloxane. The diffusive motion was found to be rouse type and restricted in space. For the first time the extent of these spatial limitations was determined experimentally. The results strongly support the concept which underlies the phantom network model.

Carbon monoxide adsorbed on clean and K-covered Ni(110) surfaces is studied by polar-angle x-ray-photoelectron diffraction to determine the C-O bond orientation relative to the surface normal. At 300 K CO adsorbs perpendicularly on clean Ni(110) with the C down, while at 120 K a high-coverage layer forms with CO tilted ±21° from normal in the [001] azimuth. The coadsorbed K/CO layer at 300 K is a mixture of tilted and perpendicular CO, the former having a tilt angle of 32° in [001] azimuth. This tilted CO is due to the K interaction and is more strongly absorbed than perpendicular CO.

We use scanning tunneling microscopy to investigate the reactivity of the dangling-bond states of Si(111)-(7×7). The reaction with ${\mathrm{NH}}_3$ is used as a prototype. We find that Si rest atoms are more reactive than Si adatoms and that center adatoms are more reactive than corner adatoms. Using atom-resolved electronic spectra, we probe the dangling-bond states on both clean and ${\mathrm{NH}}_3$-exposed surfaces. We find significant interactions and charge transfer between sites which strongly influence surface reactivity.

The effects of random impurities on the growth kinetics of oxygen chemisorbed on the W(112) surface at halfmonolayer coverage are studied by high-resolution low-energy electron diffraction. An apparent deviation of the Lifshitz-Allen-Cahn growth law of the (2×1) domains has been observed in the presence of nitrogen impurities in the early stage after the mixed overlayer is quenched from a random-lattice-gas state. An effective power law for the domain growth with R${\mathrm{¯}}^2$∼${\mathrm{t}}^{\mathrm{x}}$, where R¯ is the average size of the domain, can be established. The effective exponent x was found to decrease from 1 as the density of the impurity increased. This result is consistent with recent theoretical calculations based on a random-field Ising model.

Recent neutron-scattering data for the spin-correlation length in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ can be fitted quantitatively with an analysis of the quantum mechanical nonlinear σ model in two space dimensions. The coupling constant must be chosen in the range where an isolated ${\mathrm{CuO}}_2$ layer has antiferromagnetic order at T=0. The parameters are consistent with the spin-wave theory for the nearest-neighbor spin-(1/2 Heisenberg antiferromagnet on a square lattice.

We have measured the low-field magnetoresistance and current-voltage characteristics of polycrystalline ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ near the superconducting-normal transition. The development of a fully superconducting state occurs via an intermediate phase about 2 K in width. Within this intermediate phase, sample dissipation is highly non-Ohmic and exhibits extreme sensitivity to small magnetic fields. The nonlinear I-V characteristics describe a new phase with zero resistance and zero critical current which seems to arise from the presence of strong junction disorder.