Melting transformations in metastable quasicrystalline Al-Mn phases have been measured for the first time, by use of a new rapid electron-beam heating technique applied to surface layers with 14.8–20.5 at. % Mn. The melting temperature for icosahedral ${\mathrm{Al}}_{80}$${\mathrm{Mn}}_{20}$ is directly measured to be 910±20 °C, and is believed to be near the congruent melting point. The decagonal-phase liquidus at the same concentration is inferred to be 965±20 °C. The melting temperatures of the icosahedral phase are ∼30 °C below those of crystalline compounds of the same compositions.

We have used the depression of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ melting pressure with magnetic field to determine the magnetization of the ordered solid phases in the T=0 limit from 0.2 to 11 T. In the U2D2 phase we find that χ=(5.41±0.08)×${10}^{\mathrm{-}6}$ cgs, independent of field, while in the canted antiferromagnetic phase we are able to extrapolate the magnetization for the first time to full ferromagnetic alignment at ${\mathrm{H}}_{\mathrm{c}2}$=21.7±1 T. This field is of particular importance, as it is the only point in the ordered phases at which the results of mean-field theories, used to calculate physical properties from the Hamiltonian, become exact.

We present a neutron-scattering experiment on the static and dynamic structure factor of star polymers in dilute solution. By application of neutron spin echo, for the first time, the internal relaxation modes of such polymers could be observed directly. As the most important feature the collective dynamic response for high-functionality stars shows a pronounced de Gennes–type narrowing in the range of momentum transfer where the static structure factor in its Kratky representation exhibits a maximum. The phenomenon scales with the arm length of the star and appears to be independent of molecular weight.

A 2D Ising model in which the bonds K fluctuate randomly about ${\mathrm{K}}_{\mathrm{c}}$, the critical value of the pure system, is considered. The ensemble average of the square of the two-point function, <<${\mathrm{s}}_0$${\mathrm{s}}_{\mathrm{R}}$${\mathrm{〉}}^2$${\mathrm{〉}}_{\mathrm{Av}}$, is shown to decay as (lnR${)}^{1/4}$${\mathrm{R}}^{\mathrm{-}1/2}$ aat the critical point. This implies that <<${\mathrm{s}}_0$${\mathrm{s}}_{\mathrm{R}}$${>>}_{\mathrm{Av}}$ is bounded above by (lnR${)}^{1/8}$${\mathrm{R}}^{\mathrm{-}1/4}$ in disagreement with the exp [-(ln lnR${)}^2$] decay law found by Dotsenko and Dotsenko by a different method. On the other hand, the present calculation reproduces their specific-heat singularity C∼ln‖lnτ‖ (τ=K-${\mathrm{K}}_{\mathrm{c}}$).

We study the lowest-lying excited states of arbitrary anharmonic solids (crystalline, glassy, or amorphous). Defining the harmonic (‘‘skeleton’’) lattice underlying any such anharmonic medium, we show that its spectrum of elementary excitations provides a rigorous upper bound to that of the anharmonic medium. We then calculate upper bounds to that spectrum, in terms of an isotropic, homogeneous, harmonic medium.

We have studied the high-frequency conductivity of multilayer two-dimensional electron systems on GaAs in perpendicular magnetic fields with far-infrared transmission spectroscopy. In addition to cyclotron excitation, new resonances with energies close to the cyclotron frequency are observed. Their number and dependence on the magnetic field strength and charge density are consistent with those theoretically predicted for two-dimensional magnetic excitons.

Mossbauer-effect measurements show that for Eu metal, intermediate-valence and antiferromagnetic ordering states coexist over the pressure range 0 to 14 GPa for temperatures below the Néel temperature of about 90 K. As the average valence increases with pressure up to 12 GPa, the magnetization decreases due to a dilution of the average magnetic moment per atom.

We report evidence for superconductivity in undoped ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ obtained from resistivity, thermoelectric power, and susceptibility measurements. The onset temperature is near 40 K and we have determined its pressure and field dependence in resistivity. The superconducting behavior is of a trace and filamentary nature and is quite sensitive to stoichiometry. Its occurrence is extremely process dependent and an be controlled by oxygen pressure. We discuss several likely sources for the superconducting activity.

A new mechanism for strong Anderson localization of photons in carefully prepared disordered dielectric superlattices with an everywhere real positive dielectric constant is described. In three dimensions, two photon mobility edges separate high- and low-frequency extended states from an intermediate-frequency pseudogap of localized states arising from remnant geometric Bragg resonances. Experimentally observable consequences are discussed.

We have observed a new type of feature in electron-energy-loss spectra, which is not related to a particular discrete loss channel, although it is a peak which exhibits dispersion. Calculations show that this feature is due to the kinematical nature of the dipole scattering probability function and the unusual form of the surface response function generated by the semimetallic band structure of graphite. The peculiarly intense continuum of electron-hole pair excitations allows the loss structure to be observed.

Experimental data by diverse authors show that the ionization energies of valence levels of xenon atoms residing on pure metal surfaces or on top of a thin insulator slab are nearly constant. It is suggested that this independence of the ionization energy of the slab thickness is due to identical final states, brought about by a transfer of the valence-band hole during the photoionization process into the layer of the insulator closest to the metal.

A new method for detecting solar neutrinos and other weakly interacting particles is proposed and described. The detector consists of a large mass of superfluid helium at low temperatures (20 mK). When a neutrino is scattered off an electron, the recoil energy of the electron (${10}^{\mathrm{-}6}$ to ${10}^{\mathrm{-}7}$ erg) is deposited in the helium. This small amount of energy can be detected because of the unusual kinetics of rotons at low temperatures. It should be possible to construct a detector of sufficiently low background and large size to measure solar neutrino spectra.

Sample rotation is shown to induce frequency splittings in nuclear-quadrupole-resonance spectra. The splittings are interpreted both as a manifestation of Berry's phase, associated with an adiabatically changing Hamiltonian, and as a result of a fictitious magnetic field, associated with a rotating-frame transformation. Real and fictitious fields are contrasted. Related effects are predicted in other magnetic resonance experiments that involve sample rotation.

A new type of disorder parameters is defined. By investigation of their properties it is concluded that the $\mathrm{O}\mathrm{}\left(N\right)\mathrm{}$ nonlinear $\sigma$ models exhibit a phase transition for $D\ge 2$; similarly for gauge theories for $D\ge 3$. For continuous spins and groups the low-temperature phase contains massless excitations.

A new resonance at 1480 MeV with a width of 110 MeV is found in $\overline{p}n$ annihilations in the channel $\overline{p}n\to {\pi }^{-}{X}_0\mathrm{}\left(1480\right)\mathrm{}\to {\pi }^{-}{\rho }^0{\rho }^0$. Its mass, width, spin, and parity are shown to be consistent with the ${\rho }^0{\rho }^0$ enhancement observed in $\gamma \gamma$ reactions. Together with the suppression in the $\gamma \gamma \to {\rho }^{+}{\rho }^{-}$ data which requires the admixture of an isotensor structure, this ${\rho }^0{\rho }^0$ resonance in $\overline{p}n$ annihilation and $\gamma \gamma$ reactions and their small $\pi \pi$ branching ratios represent the best evidence yet for $Q^2{\overline{Q}}^2$ states. A ${\rho }^{-}{\rho }^{-}$ resonance in $\overline{p}n$ annihilations which would betray the exotic isotensor nature of the resonance is predicted.

We propose to study the slope parameters of $K^{+}$ and $K^{-}$ energy spectra from relativistic heavy-ion collisions in the regime of complete nuclear stopping, and suggest a characteristic change of these slopes as a signal for transition into a baryon-rich quark-gluon plasma.

The ground-state magnetization densities of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$ have been studied by 180° elastic electron scattering. The magnetic form factors were found to be quenched substantially relative to the predictions of the independent-particle model. Microscopic calculations indicate that core polarization can account for part of the observed suppression but it is not sufficient to reproduce the data. The quenching observed at high momentum transfers is comparable to that observed in related electron-scattering studies in the lead region, and can be explained in terms of partial occupancy of shell orbits in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.

We outline a method for determining independently the electron temperature and charge-state distribution in plasmas by use of ratios of sodiumlike satellite and neonlike resonance x-ray emission. The technique is applied to a bromine plasma produced by laser irradiation of a microdot. Results are consistent with the formation in the corona of a recombining plasma. The temperature is found to decrease with distance in the corona.

We have produced large-area (some square centimeters), crystallographically oriented icosahedralphase material by implanting Mn ions directly into single-crystal Al substrates. High-resolution x-ray measurements of the positions and line shapes of the quasicrystal diffraction peaks reveal systematic deviations from perfect icosahedral symmetry. A quantitative analysis of the data shows that the samples contain a simple form of phason strain field which depends on the kinetics of grain formation. The results rule out the icosatwin model proposed by Pauling.

$T_1$ measurements have been performed on the solid phase of helium-3 adsorbed on Grafoil. A theory has been developed to interpret these data on the basis of the hypothesis of a single correlation time for the exchange-induced spin motion. We infer that the relaxation is mediated by the internuclear dipolar interaction. We show how the $T_1$-minima data together with exact moment and hydrodynamic calculations may be used to approximate the spectral functions over their whole range. Thus we obtain numerical values for the exchange frequency for all regions of data. Our method is quite general and applicable to other systems.