Evidence of a magnetic-field-induced isotropic-nematic phase transition is presented for a colloidal suspension of monodisperse fd virus, a semiflexible particle with a length-to-diameter ratio of ∼140. The dynamics of the phase transition are slow enough to study the unstable portion of the phase diagram and the subsequent phase separation.

A rigorous hydrodynamic theory of the A-B transition is presented. All dissipative processes are considered. At low interface velocities, those occurring on hydrodynamic length scales, not considered hitherto, are most probably the dominant ones.

The dynamics of monoatomic steps on the Au(110) surface was studied with a scanning tunneling microscope from room temperature to 590 K. The time dependence of the position fluctuations of steps was measured as a function of temperature and kink density. The mean-square displacement of the position was found to be proportional to the square root of time. The proportionality constant exhibits Arrhenius behavior and varies linearly with the kink density. The step dynamics is dominated by the diffusion of geometrical kinks that cannot pass each other.

Equilibrium fluctuations of steps on vicinal Cu(1 1 19) surfaces show a power law time dependence. The exponent of 1/4 provides evidence that the step edges and the terraces do not exchange atoms in the investigated temperature range. The activation energy for the emission of adatoms from kink sites on to the step edges is higher than what is expected based on recent total energy calculations.

Implanted Fe atoms in hcp Zr, Ti, and Hf occupy both substitutional and interstitial lattice sites. In all three systems, substitutional Fe is found to be strongly magnetic, while interstitial Fe is nonmagnetic. First principles calculations for the magnetic properties and the isomer shift have been carried out for substitutional sites (by two independent methods) and for the interstitial sites. The theoretical predictions for both lattice sites are in excellent agreement with the exerimental results.

In this paper we present the first direct and unambiguous evidence that the total number of electrons which can be trapped on Ge-DX centers is exactly twice as large as the number of electrons which can be bound on Ge-${\mathit{A}}_1$ donor states. It should be emphasized that our reasoning does not require any technological information, about either doping or the compensation of a sample.

We show that the recently developed Chern-Simons gauge theory for fractional quantum Hall effect leads naturally to a striking prediction that an applied gate voltage coupled to an isolated region in a two-dimensional electron gas can induce Little-Parks oscillations of the longitudinal conductance in the quantum Hall devices at odd denominator filling fractions. For even denominator filling fractions, the Chern-Simons fermions are in a Fermi liquid state, and the conductance fluctuations are similar to the Aharonov-Bohm conductance oscillations of a mesoscopic metal.

Magnetoconductance fluctuations are used to extract information about frozen spin configurations in submicrometer sized CuMn wires with Mn concentrations of 320 and 1000 atomic ppm (parts per ${10}^6$). Measurements with the magnetic field parallel to the wires separate the spin and orbital field scales. At low temperatures the configurations distort reversibly over a field scale on the order of the bulk exchange field ${\mathit{H}}_{\mathit{g}}$. The data are used to map out a sample specific internal field distribution to over 30 ${\mathit{H}}_{\mathit{g}}$.

The contribution of the vortex fluctuations to the specific heat of the vortex lattice, ${\mathit{C}}_{\mathit{v}}$, in a highly anisotropic layered superconductor is calculated for the field B perpendicular to the layers in the interval ${\mathit{H}}_{\mathrm{c}1\mathrm{}}$≪B≪${\mathit{H}}_{\mathit{c}2}$. The model of the quantum overdamped oscillator for vortex vibrations is used to describe the dynamics of vortices at low temperatures. The specific heat ${\mathit{C}}_{\mathit{v}}$(T,B) is linear in temperature at low T and increases with field, ${\mathit{C}}_{\mathit{v}}$∝lnB in the case of weak pinning and ${\mathit{C}}_{\mathit{v}}$∝B in the case of strong pinning.

We propose controlled splay of artificial columnar defects in cuprate superconductors as a strategy to enhance transport properties in a field compared to parallel columns. The theory predicts a new ‘‘splayed glass’’ phase characterized by a reduced flux creep, an entangled ground state, and an astronomically slow response to an applied transverse field.

The physical contributions to the ${\mathrm{KNiF}}_3$ magnetic exchange coupling integral have been obtained from specially designed ab initio cluster model calculations. Three important mechanisms have been identified. These are the delocalization of the magnetic orbitals into the anion ‘‘p’’ band, the variational contribution of the second-order interactions, and the many-body terms ‘‘hidden’’ in the two-body operator and the Heisenberg Hamiltonian.

We report the first observation of dipolar magnetic order in a diamond lattice, in the R${\mathrm{PO}}_4$(${\mathrm{MoO}}_3$${)}_{12}$⋅${30\mathrm{H}}_2$O compounds (R=Gd, Dy, Er). Theory predicts antiferromagnetic order for a diamond lattice of dipoles, with a susceptibility at T=0 depending only on lattice symmetry and spin. We present experimental susceptibilities for ions with different effective spin which are consistent with these predictions, and which confirm the existence of unusually large quantum spin fluctuations in these materials. The fluctuations substantially exceed those of the Heisenberg antiferromagnet.

Elongated ferromagnetic single-domain particles are believed to exhibit a high stability of their remanent magnetization. However, here it is shown that for elongated particles thermal fluctuations lower the coercivity much more drastically than predicted by current theories. The rate for magnetization reversal is calculated for a classical model of a ferromagnet that allows for a spatially nonuniform magnetization distribution along the sample. The prefactor of the Arrhenius factor is explicitly evaluated and analytical results are obtained in the experimentally important limit of external magnetic fields close to the anisotropy field and for moderate damping.

DNP (dynamic nuclear polarization) experiments at 5 T are reported, in which a cycoltron resonance maser (gyrotron) is utilized as a 20 W, 140 GHz microwave source to perform the polarization. MAS (magic angle spinning) NMR spectroscopy with DNP has been performed on samples of polystyrene doped with the free radical BDPA (α,γ-bisdiphenylene-β-phenylallyl) at room temperature. Maximal DNP enhancements of ∼10 for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ∼40 for ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ are observed and are considerably larger than expected. The DNP and spin relaxation mechanisms that lead to these enhancements at 5 T are discussed.

Optically detected electron paramagnetic resonance of single molecules of pentacene in a p-terphenyl crystal at 1.8 K is presented. Transient nutation of a single electronic spin is demonstrated, showing a coherence damping within several microseconds. The fluorescence photons of a single molecule can be used as an internal timebase to trigger the application of microwave pulses. Because of this it is possible to enhance or switch off the optically detected magnetic resonance effect, depending on the delay between the triggering photon and the microwave pulse.

We describe how to separate all surface, interface, and bulk tensor components in optical second-harmonic generation experiments on isotropic thin films. Using in situ thickness scans and group theoretical arguments concerning the bulk tensor components, we demonstrate that the second-harmonic resonance of ${\mathrm{C}}_{60}$ at 2ħω=3.6 eV is of bulk character, and, quite remarkably, of magnetic dipole induced origin.

A new quantum interference phenomenon in optical absorption is reported. This effect manifests itself in a striking suppression of the absorption coefficient as a function of the electric field concomitant with a negligible Stark shift of the transition in suitably designed coupled-quantum-well semiconductors. This phenomenon, which does not arise from a reduced overlap of the final and initial states of the transition, is shown to be caused by quantum interference between two spatially separated transitions. The basic and general nature of this mechanism could be exploited in other artificially structured materials as well.

The size dependence of the contribution to the excitonic dephasing rate in semiconductor nanocrystals is clarified for various electron-phonon coupling mechanisms. On the basis of these dependencies, the commonly observed linearly temperature-dependent term of the excitonic dephasing rate and the proportionality of its magnitude to the inverse square of the nanocrystal size are attributed to pure dephasing due to deformation-potential coupling. The calculated coefficients of the linearly temperature-dependent term are quantitatively in good agreement with the experimental results on CdSe and CuCl nanocrystals.

X-ray magnetic circular dichroism (MCD) spectra and orbital angular momentum, 〈${\mathit{L}}_{\mathit{z}}$〉, for transition metal bulk and surfaces were studied for both ground state and core hole excitations using a highly precise local density approach. For Fe(001), we predict a double peak structure in both the MCD and total absorption spectra and a strong enhancement of 〈${\mathit{I}}_{\mathit{z}}$〉. Surprisingly, the MCD orbital sum rule is found to be valid to within (5–10)%. Finally, the results suggest possible solutions to several problems faced in applying the MCD sum rule to measure 〈${\mathit{L}}_{\mathit{z}}$〉.

A new class of inelastic collisional processes accounts for the electron spectra of ion-bombarded sodium halide surfaces. These spectra indicate that the deexcitation process consists of a sequence of lattice-ion collisions in which localized electron transfer occurs. Such collisional processes demonstrate how collisions can initiate electronic change in molecular compounds and that electron-transfer processes must play an essential role in chemistry activated by energetic collisions.