The ion-beam-induced epitaxial crystallization rate of amorphous Si was measured by time-resolved reflectivity on crystal substrates with orientations every 5° from (100) to (111) to (011). The measurements show that the (011) regrows 3% slower than the (100), and the regrowth rate steadily decreases with increasing misorientation towards the (111). These data can be explained using a growth-site-limited model wherein a beam-induced defect flux to the interface results in a growth-rate dependent on the interfacial bonding configuration.

The extraction of adatom-adatom interaction energies from scanning-tunneling- and field-ion-microscopy images is discussed. For the case of comparing experimental data with a solved model (e.g., Monte Carlo simulations), an expression for the expected precision is derived. It is demonstrated that in the absence of any Monte Carlo calculations the interaction energies can be extracted if measurements are made at more than one temperature. This technique requires a factor of ∼2.6 additional measurements to obtain the interaction energy to the same precision as for a solved model.

Light scattering and precision calorimetry show that the nematic ordering of octylcyanobiphenyl (8CB) filling the connected network of pores of a silica aerogel does not occur via the first-order phase transition characteristic of the bulk. Rather, ordering is continuous with an orientational correlation length never increasing beyond the aerogel pore size. The heat-capacity anomly of the second-order nematic–smectic-A phase transition seen in the bulk is absent or greatly broadened in the aerogel.

Current renormalization-group theory for critical wetting with short-range forces uses the interfacial Hamiltonian Fdy[1/2Σ${\mathrm{̃}}_{\mathrm{\infty }}$(∇l${)}^2$+W(l)] for the wall-interface separation l(y) (≫${\xi }_{\mathrm{\beta }}$, the bulk correlation length). For d=3 dimensions it has predicted strong nonuniversal singularities that are inconsistent with simulations. But we show that a variable interfacial stiffness, Σ${\mathrm{̃}}_{\mathrm{\infty }}$+ΔΣ̃(l), arises and must also be allowed for. The sign and ${\mathit{le}}_{\mathrm{\beta }}^{\mathrm{-}2\mathit{l}/\xi }$ decay of Σ̃(l) near the transition leads, for typical parameter values, to a fluctuation-induced, first-order wetting transition which may explain the simulation.

It is demonstrated that the concept of surfactant applies to the epitaxial growth of highly strained III-V semiconductors. The pseudomorphic growth regime of the InAs on GaAs(001) is extended from 1.5 to 6 monolayers by the use of Te as surfactant. This delayed plastic relaxation of the strain is correlated with the modification of the growth mode via surface energy minimization.

We present Hilbert-space basis set reduction as a novel approach to reduce the computational effort of accurate correlation calculations for large basis sets. We motivate the method by an examination of the perturbative corrections in scaling theory and present a criterion for the choice of the internal basis. The method is illustrated with two calculations for the ground state of carbon and the energy curve of the beryllium dimer: In either case the errors introduced are less than 1% of the correlation energy. The method scales as the second power of the number of the basis functions and can exploit the benefits of massive parallelization.

A new method of four-wave-mixing spectroscopy in GaAs quantum wells reveals spectral hole burning due to spin relaxation of magnetoexcitons. The measurements resolve the Zeeman doublet of the lowest-energy heavy-hole exciton where the doublet splitting is much less than the exciton inhomogeneous width. The Zeeman splitting depends nonlinearly on the magnetic field and is small compared with that of bulk GaAs. The results reflect effects of the complex band structure of quantum wells. Information on exciton spin relaxation is also provided by the hole-burning measurements.

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on the layered compound 1-T-${\mathrm{TiTe}}_2$, whose low-energy properties are those of a normal metal, and analyzed the experimental line shapes in terms of the Fermi-liquid self-energy. We find excellent agreement between the measured and theoretical spectral weight distribution, while line profiles expected for other theoretical models such as the marginal Fermi liquid clearly fail to reproduce the experimental spectra. This demonstrates that ARPES line shapes are able to reflect the nature of an interacting electron system.

Soft x-ray emission spectroscopy is for the first time applied to surfaces and adsorbates. Surface sensitivity is achieved by employing synchrotron radiation in grazing incidence for the excitation. We present O K emission from adsorbed atomic oxygen on Ni(100) and Cu(100) and molecular CO on Ni(100). The observed spectral features correspond to the occupied 2p partial density of states of the adsorbates.

The properties of the edge of a two-dimensional electron crystal in a strong magnetic field are studied in the Hartree-Fock approximation. It is demonstrated that the electrons may suffer edge reconstructions or melt at the edge, depending on the strength and nature of the potential which confines the electron system. The melting transition is signaled by the appearance of a mode in the collective excitation spectrum which is gapless in the presence of pinning centers and is localized at the edge of the system. We argue that an edge melting transition would be accompanied by a qualitative change in the transport properties of the system.

We have developed a simple method to analyze and predict the thermally stimulated current (TSC) of charged insulating thin films experiencing arbitrary time-dependent thermal environments and high electric fields. The method allows greater flexibility in experimental conditions than previous work, and includes the effect of field-induced barrier lowering on the trap energy scale. Trap distributions for irradiated metal-${\mathrm{SiO}}_{2\mathrm{-}}$Si capacitors were accurately determined from TSC measurements spanning a factor of 50 in heating rate, providing an improved estimate of trapped-hole energies in ${\mathrm{SiO}}_2$ (peak ∼1.8 eV).

We report on current-voltage measurements in clean, untwinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ single crystals with picovolt voltage sensitivity and millikelvin temperature resolution in magnetic fields ranging up to 7 T. We find evidence for a melting transition in the vortex lattice which is hysteretic in both temperature and magnetic field. The measured thermal and magnetic hysteresis widths are related by the local slope of the phase boundary. This strongly supports the picture that, in the clean limit, the melting transition of the Abrikosov vortex lattice is a first-order phase transition.

The superconductor-insulator transition at zero temperature in two dimensions is studied by Monte Carlo simulations of interacting bosons (Cooper pairs) moving in a quenched random potential. We calculate the universal conductivity ${\mathrm{\sigma }}^{\mathrm{*}}$ and the critical exponents at the superconductor-insulator transition. For the short-range repulsive case we find ${\mathrm{\sigma }}^{\mathrm{*}}$=(0.14±0.03)${\mathrm{\sigma }}_{\mathit{Q}}$, where ${\mathrm{\sigma }}_{\mathit{Q}}^{\mathrm{-}1}$==${\mathit{R}}_{\mathit{Q}}$ ==h/(2e${)}^2$≃6.45kΩ, and for long-range Coulomb interactions we find ${\mathrm{\sigma }}^{\mathrm{*}}$=(0.55±0.1)${\mathrm{\sigma }}_{\mathit{Q}}$.

A Heisenberg antiferromagnet on a kagomé lattice is highly degenerate in the classical limit. I show that quantum fluctuations lift the degeneracy and yeild the low-energy branch of spin-wave excitations with a velocity which is a factor ${\mathit{S}}^{\mathrm{-}1/3}$ smaller than for conventional spin waves. The relevance of these results to the experiments on the stacked kagomé antiferromagnet ${\mathrm{SrCr}}_{8\mathrm{-}\mathit{x}}$${\mathrm{Ga}}_{4+\mathit{x}}$${\mathrm{O}}_{19}$ is discussed.

Moriya’s expression for the ringle-bond anisotropic superexchange interaction is shown to possess an overlooked hidden symmetry, isomorphic to the symmetry of the isotropic case. For the unfrustrated case, this symmetry results in a degeneracy of the macroscopic state, implying no unique value for the Dzyaloshinsky weak ferromagnetic moment. A unique value emerges from superexchange only when more than a single bond is considered and only as a result of frustration. This implies that the symmetric part of the superexchange anisotropy tensor must vary among the bonds. The results are particularly relevant for the spin anisotropies in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$.

Magnetization measurements at ambient pressure on κ-(ET${)}_2$Cu[N(CN${)}_2$]Cl, an organic salt that is superconducting under pressure (${\mathit{T}}_{\mathit{c}}$=12.8 K at 0.3 kbar), reveal an antiferromagnetic transition near 45 K and, for the first time in this class of materials, a transition near 22 K to a state displaying weak ferromagnetic hysteresis with a saturation moment of (8×${10}^{\mathrm{-}4}$)${\mathrm{\mu }}_{\mathit{B}}$/formula. This low-temperature state is characterized by a sequence of first-order magnetization jumps.

Quantum well states are found at the Fermi level in Cu on Co(100) and Ag on Fe(100) using inverse photoemission. They appear every 5.9±0.5 layers in Cu/Co(100), which agrees with the 5.5- to 6-layer oscillation period of the magnetic coupling in Cu/Co(100) superlattices. For Ag/Fe(100) they connect with minority-spin interface states observed below ${\mathit{E}}_{\mathit{F}}$ previously, providing a magnetic coupling channel through the noble metal. These properties are explained in terms of the bulk band structure.

We present Raman scattering spectra of intrasubband excitations in an n-type modulation-doped single quantum well. We attribute a double peak in the depolarized spectra to be due to spin-flip single-particle transitions. This gives direct spectroscopic evidence at zero applied magnetic field of the spin splitting of the conduction band of GaAs due to the lack of inversion symmetry in zinc-blende compounds.

Breakup of a below-resonance femtosecond pulse is observed in a room-temperature GaAs/AlGaAs multiple-quantum-well waveguide using cross-correlation techniques. The breakup is due to neither self-induced transparency nor temporal solitons. Instead, calculations based on the coupled semiconductor Maxwell-Bloch equations show that coherent self-phase-modulation during propagation drives the system out of the initial adiabatic following regime into excitation density oscillations and eventually pulse-shape modulations.

The yield for photodissociation of ${\mathrm{Cl}}_2$ in solid Ar was measured experimentally as a function of photon energy and studied by molecular dynamics simulations. The results show that separation of the Cl fragments at low energies occurs by delayed exit (t≳3 ps) from the surrounding cage of Ar atoms. Above a photon threshold energy of ≳9.0 eV, there is a switchover to direct cage exit, in which the Cl impulsively knocks a cage atom out of its way. The results are a first demonstration of delayed cage exit and of changeover from delayed to direct exit in solid-state photolysis.