We study mesoscopic conductance fluctuations in the metallic phase of the integer quantum Hall effect. We derive effective boundary conditions for the diffuson propagator which incorporate the edge-state transport along the sample boundaries. It is shown that the presence of edge states leads to a resonance structure in the conductance fluctuations which occurs as the Fermi level moves across the band of extended states. The result of this analytic treatment is consistent with that of our numerical simulations and can be tested experimentally.

The problem of an electron gas interacting via exchanging transverse gauge bosons is studied using the renormalization group method. The long wavelength behavior of the gauge field is shown to be in the Gaussian universality class with a dynamical exponent z=3 in dimensions D≥2. This implies that the gauge coupling constant is exactly marginal. Scattering of the electrons by the gauge mode leads to non-Fermi-liquid behavior in D≤3. The asymptotic electron and gauge Green’s functions, interaction vertex, specific heat, and resistivity are presented.

We have observed two-state systems (TSSs) in electrically stressed metal-oxide-silicon field-effect transistors, by studying random telegraph signals at low temperatures. The TSSs are related to defects close to the Si/${\mathrm{SiO}}_2$ interface. The asymmetry energy ɛ is linear in gate voltage, permitting for the first time measurement of the dissipative tunneling rate as a function of ɛ independently of magnetic field. The electron coupling strength α lies in the range ${10}^{\mathrm{-}3}$ to ${10}^{\mathrm{-}2}$, allowing comparison with the standard theory in the previously unexplored regime of weak coupling.

A novel representation is derived for the microscopic partition function of two-dimensional electrons confined to the lowest Landau level. The dynamics is described by the two-component quantum plasma of particles and holes. We find a topological term in the Euclidean microscopic action to be dynamically generated in this representation. Starting from this partition function we find uniform solutions of the equations of motion only at ν=(2k+1${)}^{\mathrm{-}1}$. At these special filling fractions the Chern-Simons theory arises as a saddle-point approximation to the microscopic action.

We present a rigorous proof that the ground state of a negative-U Hubbard model on some bipartite lattices Λ possesses off-diagonal long-range order in a finite range of the electron filling factor ${\mathrm{\rho }}_{\mathit{e}}$.

The force-displacement response of vortices pinned in epitaxial YBCO thin films has been determined using an ac transport technique. The effective curvature of the pinning wells and the elastic limit of the displacement of the vortices before depinning are obtained. For magnetic fields parallel to the c axis the elastic limit is about a coherence length, consistent with core pinning. When the field is applied parallel to the ab planes structure appears in the force-displacement curve before the onset of flux flow. These ‘‘steps’’ appear at vortex displacements which are closely related to the spacing between the superconducting layers, providing direct evidence for intrinsic pinning.

The effects of columnar pins on the flux lines in a model high-${\mathit{T}}_{\mathit{c}}$ superconductor in an applied field are studied through Monte Carlo simulations. An analytic solution for a single line case is obtained and compared with the simulation results. By introducing a tilted potential, we study simulated ‘‘I-V’’ characteristics and the results indicate a distinct scaling behavior above and below the depinning temperature. We introduce a diverging length scale measured in terms of a ‘‘retrapping length’’ to analyze self-similar behavior across the sharp depinning crossover.

Recent magnetic resonance experiments on ferritin and nanofabricated magnetic dots of Fe(CO${)}_5$ have been interpreted in the framework of macroscopic quantum coherence (MQC). The power absorption in MQC is calculated and shown to be exceeded by a factor of 50 to 150 in the ferritin experiments. Alternative microscopic causes for the resonance are suggested. In the Fe(CO${)}_5$ experiments, MQC predicts no resonance at all at the ac fields involved, and the power absorbed is ${10}^{18}$ times larger than expected.

We calculate the RKKY coupling between two magnetic layers separated by a nonmagnetic spacer, with scattering potentials added to represent changes in environment between the layers. For the case of a spacer potential well of depth V, the usual π/${\mathit{k}}_{\mathit{F}}$ oscillation period is superseded by one much longer, πħ/ √2mV . For a deep potential well (V∼${\mathrm{\varepsilon }}_{\mathit{F}}$), the RKKY interaction becomes purely ferromagnetic for spacings greater than a few angstroms. Scattering potentials localized at the interfaces produce a phase shift in the RKKY oscillations. We discuss evidence for these effects in experimental systems.

Spectral diffusion of the transition frequency of single pentacene molecules in p-terphenyl crystal was recently observed experimentally. In this Letter we propose a microscopic theoretical model to explain this phenomenon. Analysis of the experimental data with our model yields detailed microscopic information about the nature and spatial distribution of the localized excitations responsible for the observed spectral diffusion.

Ultraviolet photoelectron spectra (UPS) of ${\mathrm{LaC}}_{82}$ questioning whether the La atom is inside the C cage or not are measued for the first time. The UPS of ${\mathrm{LaC}}_{82}$ is analogous to those ${\mathrm{ofC}}_{82}$ but there is a critical differnce in the region just below the Fermi level. It is on appearance of two new peak components at 0.9 and 1.6 eV with the intensity ratio of 1:2 in the UPS of ${\mathrm{LaC}}_{82}$. Their origin is the transfer of three electrons from La to ${\mathrm{C}}_{82}$ to form the electronic structure of ${\mathrm{La}}^{+3\mathrm{}}$${\mathrm{C}}_{82}^{\mathrm{-}3}$. Present results combined with theoretical calculations on the position of the La atom in the molecule assert an encapsulation of the La atom inside the C cage.

A binary lattice model with hard-repulsive interactions is presented consisting of hexagons and points on a two-dimensional triangular lattice. This is the first model with hard interactions only to show gas, liquid, and solid phases. The phase diagram is calculated.

Equilibrium sedimentation profiles of concentrated suspensions of charged colloids are accurately determined by measuring the intensity of the depolarized light scattered by optically anisotropic particles. From the data we derive the osmotic pressure Π versus the particle volume fraction Φ. The Π(Φ) values obtained with strongly screened colloids are in excellent agreement with the predicted hard-sphere equation of state. The data show that, besides gravitation, there is an additional force acting on the particles, probably due to the buildup of an electrostatic sedimentation potential.

We propose a spin model for idiotypic–anti-idiotypic immunological networks in which each spin interacts with its mirror image spin and the neighbors of the image. We show that the critical properties of this model belong to the universality class of the Ising model, and that self-orgnaizations, large homogeneous domains formed in the biological systems, are equivalent to spinodal decomposition. Since an immunological model has to be a 5–10 dimensional space for realistically representing the shape space, the space of all possible cell configurations, this represents the first application of an Ising model above its upper critical dimension ${\mathit{d}}_{\mathit{u}}$=4.

We report a new two-photon polarization correlation experiment for realizing the Einstein-Podolsky-Rosen-Bohm (EPRB) state and for testing Bell-type inequalities. We use the pair of orthogonally polarized light quanta generated in type-II parametric down-conversion. In a 1 nm bandwidth, we observe from the output of a 0.5 mm β-${\mathrm{BaB}}_2$${\mathrm{O}}_4$ crystal the EPRB correlations in coincidence counts, and measure an associated Bell inequality violation of 22 standard deviations.

We apply a generalized transfer-matrix method to the d=2 Ising ferromagnet at H≠0 and T<${\mathit{T}}_{\mathit{c}}$ to obtain complex constrained free energies. Although the method does not explicitly introduce droplets, the imaginary parts of those constrained free energies that correspond to the metastable state are accurately predicted by a field-theoretical droplet model. The free energy of a critical droplet is given by an equilibrium Wulff construction, and we find evidence for Goldstone modes on its surface. These results indicate that our approach provides a nonperturbative numerical continuation of the free energy around the essential singularity at H=0.

A simple direct explicit proof of the generalized second law of black hole thermodynamics is given for a quasistationary semiclassical black hole.

We argue that the two-dimensional O(N)-invariant lattice σ-model with mixed isovector-isotensor action has a one-parameter family of nontrivial continuum limits, only one of which is the continuum σ-model constructed by conventional perturbation theory. We test the proposed scenario with a high-precision Monte Carlo simulation for N=3,4 on lattices up to 512×512, using a Wolff-type embedding algorithm. The finite-size-scaling data confirm the existence of the predicted new family of continuum limits. In particular, the ${\mathrm{RP}}^{\mathit{N}\mathrm{-}1}$ and N-vector models do not lie in the same universality class.

In a search for the decay ${\mathit{K}}_{\mathit{L}}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$, no candidates have been observed. We determine the sensitivity from the detected number of CP-violating ${\mathit{K}}_{\mathit{L}}^0$→${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$ decays and place a 90% confidence level upper limit on the branching ratio of B(${\mathit{K}}_{\mathit{L}}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$,‖${\mathit{M}}_{\mathit{K}}$-${\mathit{M}}_{\mathit{e}\mathit{e}}$‖<6 MeV/${\mathit{c}}^2$)≤4.1×${10}^{\mathrm{-}11}$. This result is a significant improvement over previous measurements, although still above the standard model prediction of 3×${10}^{\mathrm{-}12}$.

We report the results of a search for the decay ${\mathit{K}}_{\mathit{L}}$→${\mathrm{\pi }}^0$${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$ conducted by E799 at Fermilab. This decay mode is expected to have significant CP-violating contributions and a direct measurement could either confirm the standard model mechanisms for CP-violation or point to physics beyond the standard model. No such events were seen. The 90% confidence level upper limit is determined to be B(${\mathit{K}}_{\mathit{L}}$→${\mathrm{\pi }}^0$${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$)<5.1×${10}^{\mathrm{-}9}$.