For certain ceramic samples of the Bi-based high-temperture superconductors, the dc-field-cooling signal becomes paramagnetic in fields below a few 100 mOe. This effect correlates with an anomaly in the low-field microwave absorption. The data are consistent with orbital paramagnetic moments due to the appearance of spontaneous supercurrents in fields smaller than the lower critical field ${\mathit{H}}_{\mathit{c}1\mathit{a}}$ parallel to the CuO planes.

We report the results of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR measurements on ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_3$${\mathrm{C}}_{60}$ in the normal and superconducting states. Electronic densities of states at the Fermi energy in the normal-state and energy gaps in the superconducting state are estimated from spin-lattice-relaxation data. Implications of the relaxation and spectral data for the electronic properties of these materials are discussed.

The exact solution via Bethe’s ansatz to a model consisting of two parabolic bands of electrons with local attractive and repulsive interactions is presented. Some low-temperature properties of this model are discussed as a function of the interaction strength, a magnetic field, and the crystal-field splitting between the bands. The attractive interaction leads to Cooper-pair-like bound states and a threshold magnetic field is required to overcome the binding energy. The low-T specific heat is proportional to T, except at critical points where C∝${\mathit{T}}^{1/2}$.

Using a SQUID-based technique, we measure the Lorentz force needed to depin a single trapped vortex in a superconducting Nb strip. The vortex is trapped by heating a portion of the strip above its critical temperature ${\mathit{T}}_{\mathit{c}}$ with a laser pulse. Between 3.0 and 5.5 K, the pinning force obeys a power law ${\mathit{f}}_{\mathit{p}}$=${\mathit{f}}_{\mathit{p}}$(0)(1-T/${\mathit{T}}_{\mathit{c}}$${)}^{\mathit{n}}$, where ${\mathit{f}}_{\mathit{p}}$(0)=(4.1±0.4)×${10}^{\mathrm{-}4}$ N/m and n=1.9±0.1. We have determined at a confidence level of 99.2% that we trap single vortices, rather than multiple vortices or vortex-antivortex pairs.

The magnetic-field penetration depth λ in the organic superconductors κ-(BEDT-TTF${)}_2$ Cu(NCS${)}_2$ and κ-(BEDT-TTF${)}_2$ Cu[N(CN${)}_2$]Br has been measured over a wide temperature region 20 mK≤T≤15 K via the muon-spin-relaxation technique. Linear variation of λ with T at low temperatures, found in both systems, is consistent with anisotropic superconducting pairings with line nodes in the energy gap. In the latter compound, we observe flux depinning at T∼5 K, well below ${\mathit{T}}_{\mathit{c}}$=12 K.

A tiny in-plane XY anisotropy λ=0.02 could induce a substantially high Kosterlitz-Thouless phase transition at ${\mathit{kT}}_{\mathit{c}}$/J=0.25 in the 2D spin-1/2 antiferromagnet. Examination of transverse and longitudinal correlations indicates a Heisenberg-to-XY crossover near ${\mathit{T}}_{\mathit{c}}$, with a scaling relation suggesting an ordering transition at ${\mathit{T}}_{\mathit{c}}$∼250 K for the anisotropies measured in the undoped high-${\mathit{T}}_{\mathit{c}}$ copper oxides. The results also have implications for Kosterlitz-Thouless condensation in general 2D quantum systems.

Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone. The ${\mathrm{\Delta }}_2$ band exchange splitting (0.85 eV) and dispersion (0.5 eV) are in reasonably good agreement with self-consistent local-spin-density–approximation calculations. The conduction-band magnetic exchange splitting vanishes at the Curie temperature following a conventional power law with a Heisenberg critical exponent. This ‘‘Stoner-model’’ collapse of the exchange splitting is in striking contrast to corresponding results observed in transition-metal ferromagnets.

Absorption and emission edge singularities are calculated in the presence of a nonequilibrium Fermi sea ${\mathrm{\mu }}_1$–${\mathrm{\mu }}_2$ instead of 0–μ. The result is used to derive the absorption spectra of highly excited semiconductors. It is also of importance in the problem of x-ray-like singularities as it shows that the well-accepted physical interpretation proposed by Hopfield is actually invalid.

For a system of coplanar electrons and holes the photoluminescence spectrum in the fractional quantum Hall regime does not exhibit anomalies associated with the fractional quantum hall effect. However, when electron and hole layers are separated, a new peak in the photoluminescence spectrum is introduced when the filling factor exceeds a fraction ${\nu }_0$ at which an cincompressible state occurs. The new peak is separated from the main spectral feature by the quasiparticle-quasihole gap and corresponds to a process in which a fractionally charged quasiparticle recombines with a hole, leaving behind fractionally charged quasiholes.

A new magneto-optical sum rule is derived for circular magnetic dichroism in the x-ray region (CMXD). The integral of the CMXD signal over a given edge allows one to determine the ground-state expectation value of the orbital angular momentum. Applications are discussed to transition-metal and rare-earth magnetic systems.

The process of oxide formation at various temperatures in the range 25–300 °C on a well-defined Fe(100) surface up to oxide thicknesses of 4 nm has been investigated using HEIS, NRA, AES, and ellipsometry. The conditions for the applicability of the oxidation theory of Fromhold and Cook are met and this theory is compared to the data. The several stages with their rate-limiting steps are identified. In the regime where the oxidation rate is governed by the thermionic emission current across the metal-oxide interface, the oxidation process is described in a quantitatively adequate manner.

The force as a function of separation is measured between two mica surfaces coated with adsorbed bilayers of cetyltrimethylammonium bromide (CTAB) and immersed in aqueous ionic micellar solutions of CTAB. At low separations double-layer forces are observed and arise soley from the dissociated counterions and free ${\mathrm{CTA}}^{+}$. At large separations, the repulsion is reduced and a secondary minimum in the interaction potential deepens when the micellar concentration is increased. Finally, at higher concentrations, structural effects superimpose an oscillatory force profile at further separations.

The force as a function of separation between two mica surfaces immersed in a reversed micellar system sodium bis(2-ethyl hexyl) sulfosuccinate (AOT)/water/heptane was measured for a range of concentrations with size and polydispersity of the micelles remain constant. Measurements were carried out with a piezoelectric bimorph force sensor which produces a charge proportional to the applied load. At low micellar volume fractions the force is a purely attractive van der Waals interaction, while at higher concentrations the force-distance profile oscillates with a period equal to the size expected for the micelles. The measured interaction is lower in magnitude than theoretical values for a monodisperse hard-sphere fluid between hard walls.

We construct a partition function of N anyons in a constant external magnetic field and in an external harmonic potential well. From this we find an equation of state for the free anyon gas. The equation of state exhibits quantum behavior when the density of the anyons is of order of 1/N${\lambda }_{\mathit{T}}^2$, where ${\lambda }_{\mathit{T}}$ is the mean thermal wavelength.

Intermittent behavior originating in a point of discontinuity in 1D maps is investigated. Studying the duration of the laminar phase, we find a logarithmic dependence of the average laminar length 〈l〉 on the control parameter ε, in contrast to the three conventional types of intermittency characterized by power-law scaling. Analytical considerations give the relation 〈l〉=log(ε)/log(s)+β (where s is the ‘‘slope’’ at the point of discontinuity). Numerical data obtained from a relaxation oscillator model are in good agreement with these results.

Numerical tests of a novel semiclassical quantization rule are carried out for three strongly chaotic systems: the hyperbolic billiard, Artin’s billiard, and the Hadamard-Gutzwiller model. The results demonstrate that this novel rule is very effective and capable of generalizing sensible approximations to the quantal energy levels.

At each of three frequencies ω/2π=26.43, 30.36, and 36.02 GHz, we observe 3d hydrogen atoms with certain principal quantum numbers ${\mathit{n}}_0$≫1 to be more stable against microwave ionization. Which ${\mathit{n}}_0$’s are more stable differs for each ω. Even when the enhanced stability is not found in 3d classical calculations, we show that it scales classically: This quantal effect occurs at certain values of the classically scaled frequency ${\mathit{n}}_0^3$ω. Our data give strong support for the enhanced stability being due to scarred 3d wave functions for the strongly driven atoms.

Mori theory leads to in(finite) continued fractions [I(F)CF’s] which upon inverse Laplace transformation (ILT) give the dynamical correlations in Hamiltonian systems. We propose a direct summation method to evaluate these ICF’s, e.g., 1/[z+${\mathrm{\Delta }}_1$/(z+... ∞)], by replacing them with FCF’s with poles L=${10}^{\mathrm{\zeta }}$, 2≤ζ≤5, for ${\mathrm{\Delta }}_{\mathrm{\mu }}$=${\mathrm{\mu }}^{\mathrm{\phi }}$, φ<2. Long-time dynamics is obtained upon an ILT of the ICF for 0≤t≤τ with τ=f(φ,ζ) being large. Our studies on dynamical correlations for boundary spins in S=1/2 XY chains agree very well with a recent exact solution for these correlations.

We calculate three- and four-point functions in super Liouville theory coupled to a super Coulomb gas on world sheets with spherical topology. We first integrate over the zero mode and assume that a parameter takes an integer value. We find the amplitudes, give plausibility arguments in favor of the result, and formally continue the parameter to an arbitrary real number. Remarkably, the result is completely parallel to the bosonic case.

We numerically study the thermal nucleaton of kink-antikink pairs in (1+1)-dimensional classical field theory coupled to a heat bath. We study the dependence of the kink lifetime and number density on temperature and on the coupling to the heat bath (viscosity). We qualitatively confirm Kramers’s prediction of the viscosity dependence, and find a slight reduction in the effective kink mass compared with its zero-temperature value. We find no suppression of kink production beyond the Boltzmann factor, and we confirm a recent prediction of the renormalization of the barrier at high viscosity.