The damaged layer induced in a silicon crystal by surface scratching at room temperature under a light load was found, by transmission electron microscopy, to be a small amorphous region surrounded by a dislocated crystalline region. No dent was detected on the surface and no crack was developed around the scratch. The amorphous region seems to be formed by phase transformation and not as the result of heavy plastic deformation of the crystal. The amorphous region was recrystallized to a dislocated crystalline region by annealing of the crystal at 600 °C.

We have observed that at temperatures below 200 mK quantized vortices are created by a new process which is not described by the thermal activation theory of vortex nucleation. The critical flow velocity in a submicron orifice has been determined using two techniques. Down to about 200 mK the critical velocities rise linearly with falling temperature. Below this temperature the critical velocity stops rising and becomes almost temperature independent, indicating that a new process, possible quantum tunneling, dominates the phase-slip nucleation.

Flow measurements in ultrapure ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ through a micron-size orifice at millikelvin temperatures show, for the first time, the transition from thermal to quantum nucleation of nanometer-size vortices below a crossover temperature of 0.147 K. These observations establish the close relationship between this type of critical flow and negative-ion motion in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and strongly suggest that the underlying mechanism, the nucleation of vortex half-rings, is identical.

The first path-integral calculations of the properties of a strongly correlated continuum fermion system are described. The paths are restricted to the region of phase space with a positive trial density matrix, thereby avoiding the fermion sign problem. This restriction is exact if the nodes of the trial density matrix are correctly placed, but otherwise gives a physically reasonable approximation generalizing the ‘‘fixed-node’’ approximation used at zero temperature. Computations show that restricting the walks with the noninteracting density matrix gives good results for liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ above 1 K. Using imaginary-time-independent nodes or not allowing atomic exchange results in substantially poorer agreement with experimental energies.

We report the results of the first systematic study of the phase separation from supersaturated ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He liquid mixtures of dilute phase in the temperature range from 130 mK down to 400 μK. We find that the degree of critical supersaturation becomes almost temperature independent below about 10 mK while it increases with temperature above about 10 mK.

The spatially inhomogeneous thermal decomposition of monolayer thick oxide films on Si(001) has been investigated. After partial desorption, uniformly distributed voids are formed in the oxide layer. Analysis of the evolution in the void area distribution with extent of desorption suggests that the rate determining step in void growth is the creation of a diffusing Si monomer within the void. This explains the unexpected substantial rearrangement of the Si substrate upon desorption of a single monolayer of oxygen.

The concept of a Luttinger liquid in 1D is extended to include twisted boundary conditions on a ring and mesoscopic parity effects due to evenness and oddness of the particle number ${\mathit{N}}_0$. Using Haldane’s notion of topological excitations, a proof of Leggett’s conjecture is presented, stating that the ground state of interacting 1D quantum systems is diamagnetic or paramagnetic depending on the parity of ${\mathit{N}}_0$. The persistent currents produced by an Aharonov-Bohm flux are calculated and shown to have period and amplitude that are in agreement with recent experiments.

Strong enhancement of acoustic plasmons in optically excited nonequilibrium electron-hole plasmas in bulk semiconductors is shown to cause ultrashort (∼10 fs) dephasing times and very high carrier-carrier scattering rates.

Quasienergy minibands in superlattices which interact with intense far-infrared laser radiation collapse under conditions that are experimentally accessible. In particular, it is shown that the miniband width becomes close to, but not identical to, zero if the ratio of the Bloch frequency and the laser frequency approaches a zero of the Bessel function ${\mathit{J}}_0$.

Transmission measurements on superconducting ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ films with circular polarized light show optical activity proportional to magnetic-field strength. The results are discussed within the context of cyclotron (diamagnetic) resonance of the superconducting ground state. Hole conduction is implied.

Inelastic neutron scattering measurements over a wide Q-E range have been performed on superconducting ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. Fine structure in its phonon density of states as well as the Q dependence of excitations was revealed by means of a high-energy-resolution chopper spectrometer at a pulsed neutron source. The temperature dependence showed an anomalous behavior at ${\mathit{T}}_{\mathit{c}}$ similar to critical phenomena, which could be due to a local distortion and an expansion of the dynamical correlation length. The distortion is associated with a 〈110〉 buckling structure, which is commonly observed in the orthorhombic phase of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_4$ and in ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ in the superconducting state.

We present a semiclassical theory of charged interacting anyons in a strong magnetic field. We apply this theory to a number of few-anyon systems including two interacting anyons in the presence of an impurity and three interacting anyons. We discuss the dependence of their energy levels on the statistical parameter and find regions in which this dependence follows very different patterns. The semiclassical arguments allow us to correlate these patterns with the change in the character of the classical motion of the system.

Extensive spin-dynamics simulations have been performed to study the dynamical behavior of the classical Heisenberg chain at infinite temperatures and long wavelengths. We find that the energy and spin show distinctly different dynamics in the isotropic system. The energy correlation function follows the classical diffusion theory prediction, namely, it decays exponentially with ${\mathit{q}}^2$t. In contrast, the spin correlation function is found to decay exponentially as ${\mathit{q}}^{2.12}$t lnt, implying a logarithmically divergent diffusion constant and the failure of the usual hydrodynamic assumptions.

For an itinerant system of electrons we develop a first-principles theory of spin fluctuations. It is based on the idea of a generalized Onsager cavity field which varies slowly compared to the motion of individual electrons. It gives an account of both the good local moment and the weak itinerant ferromagnet limits within the same framework. We illustrate its consequences by explicit calculations for Fe and Ni.

We have measured the electrical resistivity through the magnetic phase transition of the nuclear spins in the Van Vleck paramagnet ${\mathrm{PrCu}}_6$ with varying frequencies and applied magnetic fields. The electrical resistivity starts to decrease at the transition temperature ${\mathit{T}}_{\mathit{c}}$ and becomes constant well below ${\mathit{T}}_{\mathit{c}}$. This resistivity decrease is found to be caused by the ferromagnetic alignment of the nuclear spins. We have also observed a critical phenomenon just above ${\mathit{T}}_{\mathit{c}}$. This critical phenomenon can be explained by a simple calculation.

For optical activity, we have derived a band-theoretic formula and evaluated it within the self-energy-corrected local-density-approximation approach using a plane-wave basis. For optically uniaxial, trigonal selenium, we compute (i) ρ, the optical rotatory power for propagation along the optic axis, (ii) ${\mathit{g}}_{11}$, a gyration tensor component, (iii) ${\mathit{d}}_{11}$ for second-harmonic generation, and (iv) ${\mathrm{\varepsilon }}_{\mathit{e}}$ and ${\mathrm{\varepsilon }}_{\mathit{o}}$, the two dielectric constants. These comprehensive results are the first reported in the literature for any crystal, and they agree with some, but not all, available measurements which are often not consistent with each other.

Fast HD molecules are observed in the reaction of a beam of H(D) aotms with D(H) atoms chemisorbed on a Cu(111) surface at 100 K. The mean kinetic energy of these molecules is close to 1 eV, or about half of that available. Angular distributions of the nascent HD product are relatively sharp, are displaced slightly away from the surface normal in the specular direction, and display a small sensitivity to the incidence energy. Both the energy and angular distributions are different for D on H and H on D. Results are discussed in terms of a direct Eley-Rideal mechanism.

We investigate the statistical properties of the surface of thin films grown by molecular-beam epitaxy (MBE). We present and analyze a simple model of MBE growth which incorporates surface diffusion and deposition in a physically correct manner. The short-time behavior does not correspond to that predicted by the continuum model of Villain, Das Sarma, and others. At long times, the model is governed by Kardar-Parisi-Zhang dynamics.

A new way of investigating the elastic field around a ledge of a faceted interface is proposed for crystalline materials. The length and/or angular misfits along two adjacent facets are accommodated by slightly deforming the atomic structural units with an appropriate distribution of translation dislocations. The Burgers vector content of the ledge is not defined as usual from a circuit crossing the interface twice, a method which proves to be sometimes misleading. An example treats, at the atomic scale, an unusual ledge of the interface TiAl/${\mathrm{Ti}}_3$Al.

The Gordon-Kim electron gas model is generalized to include a dipole polarization of the ions. The expression for the total energy of ionic crystals is derived including its polarization part. The frequencies of LO and TO phonons at the Γ point are calculated. Good agreement with experimental data for a number of alkali halides is obtained.