The novel phenomenon of exchange of stability among periodic orbits is studied with a view of understanding the recurrence of Kolmogorov-Arnol’d-Moser tori in Hamiltonian systems. This leads to a very complex phase diagram in the extended Frenkel-Kontorova model with cascades of first-order transitions separating nearby competing commensurate ground states. The Farey route to a given rotation number allows a very simple universal additive rule for constructing the phase diagram and understanding the self-similar structure underlying the nobel incommensurabilities.

Intrachain and interchain excitations are clearly identified by polarized time-resolved absorption studies of photoinduced midgap bands in well-aligned trans-polyacetylene. We report spectroscopic evidence of the lattice deformation during intrachain photogeneration of charged soliton pairs, and see these pairs recombine geminatley in <2 ps. For incident polarization perpendicular to the chain direction, our data also show that interchain electron-hole pair excitation occurs with fairly high quantum yield and leads to polaron formation.

A Green’s-function approach is employed to calculate the electron tunneling through a double-barrier device for infrared-radiation detection. Electrons photoexcited by an ir beam undergo transitions to a resonant channel, so that the transmission coefficient for tunneling substantially increases by several orders of magnitude compared with the dark state. This photon-induced resonant tunneling can be switched and controlled by a change of the applied static voltage. Such a system is ideal for ir photodetectors.

The eigenstates of electrons interacting in quantum dots in a magnetic field are studied. The interaction has important effects on the magnetic-field dependence of the energy spectrum. However, when the confinement potential is quadratic, the optical excitation energies of the many-body system are exactly the same as those of a single electron. This makes the interaction effects difficult to observe directly but they could be seen by measuring the thermodynamic properties of the electrons. This is illustrated with the calculations of the electronic heat capacity.

Surface-acoustic-wave propagation on high-quality AlGaAs/GaAs heterostructures containing a two-dimensional electron system has been examined in the fractional quantum Hall effect (FQHE) regime. The response of the electron system to the sound wave is found to be similar in the FQHE states to that previously studied in the integral quantum Hall states. However, a striking disparity is observed at Landau-level filling ν=1/2, where sound propagation is distinctly different from that in the neighboring filling-factor range. We propose that phase separation of the 2DEG may be responsible for the feature at ν=1/2.

When holes are doped into a two-dimensional antiferromagnet the spin excitations are renormalized. This renormalization is calculated for finite hole densities. The spin-wave spectrum is found to soften instantaneously upon doping, and the spectral functions are significantly broadened. With 0.1 hole per site the spin-wave spectrum collapses. The implications on the hole mobility is discussed briefly.

The Hubbard model possesses a SU(2) pseudospin symmetry, which contains the U(1) phase symmetry as a subgroup. The existence of such symmetry leads to interesting experimental consequences if the U(1) phase symmetry is spontaneously broken, i.e., if the ground state is superconducting. In this case, there must exist a pair of massive collective modes which together with the usual Goldstone mode form a triplet representation of the psuedospin group. These collective modes are collisionless and couple directly to external charge disturbances with wave number π and can therefore be detected experimentally as sharp resonances.

We have measured the amount of nonreciprocal circular birefringence of 50 to 800 Å ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ films in transmission with a 15-μm beam diameter. A novel instrument with a sensitivity of 2 μrad for nonreciprocal phase shifts was developed by modifying a fiber-optic gyroscope. It is insensitive to reciprocal phase shifts. We observed no nonreciprocal phase shifts in any samples.

The Shoji-Nishiyama mechanism prescribes a way of continuously distorting an fcc into an hcp structure. We show that the atomic displacements of this deformation mechanism can be considered as the sum of a modulation and a strain. A transition path between these two structures can therefore be characterized by a parametrization of the modulation and strain amplitudes. The free energy as a function of these two amplitudes is shown to be highly constrained and, in particular, is invariant under a two-dimensional space group.

A general concept of holonomy scattering is defined. It applies, among other things, to imply a nontrivial (generally, inelastic) scattering amplitude for the scattering of pure flux tubes off one another, when these fluxes are non-Abelian and do not commute. The amplitudes for such processes, as well as the original Aharonov-Bohm cross section, are calculated directly from an expression for the propagator with a definite winding number.

Concentrated solutions of inverted micelles show highly unusual behavior in electrical conductivity and dielectric relaxation. The conductivity shows a nearly quadratic dependence of micellar volume fraction; a departure from this behavior is seen at high volume fractions accompanied by the appearance of a new and slow dielectric relaxation process that coexists with a faster (single-particle) relaxation process. The results suggest the formation of a large scale structure of micellar aggregates.

We discuss a new extended-inflationary scenario evading the difficulties of the original model. Our model can thermalize the energy in the bubble walls by the necessary epoch, and establish a Robertson-Walker frame in the bubble clusters. The essential new ingredient in our model is the observation that the coupling of inflaton to the Jordan-Brans-Dicke field is expected to be different from that of visible matter.

It is shown that if Higgs-boson exchange mediates CP violation a significant electric dipole moment for the electron can result. Analogous effects can contribute to the neutron’s electric dipole moment at a level competitive with Weinberg’s three-gluon operator.

Fission-fragment angular distributions in reactions of ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{232}$Th and ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{237}$Np have been measured. While the measured anisotropies in B- and C-induced fission are found to be in agreement with the predictions of the standard Halpern-Strutinsky theory, they are anomalously large in the case of O- and F-induced fission. Such a discontinuous behavior in angular anisotropy with respect to the entrance-channel mass-to-charge asymmetry provides an experimental verification of the predictions of the preequilibrium fission model proposed earlier to explain the anomalous fragment angular distributions.

We have observed the channeling of cooled Na atoms in the three-dimensional interference pattern of the light fields in an optical trap. The channeling occurs for length scales from less than 50 μm up to several mm. This channeling may explain the anomalously long lifetimes observed in many such traps. We suggest that these observations may be understood in terms of a multilevel atom in the trapping light field.

We have used a heterodyne technique to observe the spectrum of resonance fluorescence from sodium atoms in optical molasses. The spectra show a very narrow feature which we attribute to Dicke narrowing of the fluorescence from atoms localized to less than an optical wavelength in three-dimensional standing-wave potential wells.

We demonstrate that for centrosymmetric structures of chiral molecules the interaction with circularly polarized light gives rise to nonzero second-order susceptibilities. It is ascribed to transitions that are both magnetic and electric dipole allowed. Experimental demonstration is given of second-harmonic generation from centrosymmetric crystals of R,S-N-acetyl valine (P$2_1$/c) using a fundamental wave having elliptic polarization in most parts of the trajectory through the crystal. These results demonstrate the existence of optical activity in the hyperpolarizability term β, similarly to the well-known optical-rotation phenomena in the linear polarizability.

An increase in the global energy confinement time (${\mathrm{\tau }}_{\mathit{E}}$) was obtained in the CTX spheromak by replacing the high-field-error mesh-wall flux conserver with a low-field-error solid-wall flux conserver. The maximum ${\mathrm{\tau }}_{\mathit{E}}$ is now 0.18 ms, an order of magnitude greater than previously reported values of ≲0.017 ms. Both ${\mathrm{\tau }}_{\mathit{E}}$ and the magnetic energy decay time (${\mathrm{\tau }}_{\mathit{W}}$) now increase with central electron temperature, which was not previously observed. These new results are consistent with a previously proposed energy-loss mechanism associated with high edge helicity dissipation.

The flow properties of concentrated suspensions having crystalline order at rest are reported. The suspensions contain charge stabilized particles and the softness of particle interaction is altered by varying the suspending phase ionic strength. The suspensions display a yield stress ${\mathrm{\tau }}_{\mathit{y}}$, and for stresses larger than ${\mathrm{\tau }}_{\mathit{y}}$, shear thin. At a critical shear stress, suspension viscosity discontinuously drops 1–3 orders of magnitude. The scaling of critical stress, yield stress, recoverable strains, and zero-frequency modulus on volume fraction and ionic strength are discussed.

Fluctuation-induced transitions between coexisting periodic attractors have been investigated with an analog electronic circuit model. Calculations and measurements of the spectral densities of fluctuations have revealed superimposed twin-peaked partial spectra and a supernarrow spectral peak whose intensity depends critically on the distance from the phase transition where the populations of the attractors equalize.