The influence of a magnetic field on the tunneling of an electron out of a confining plane is studied by a path integral method. We map this 3D problem onto a 1D one, and find that the tunneling is strongly affected by the field. Without a perpendicular field, the tunneling at zero temperature can be completely suppressed by a large parallel field, but in the small parallel field and low temperature limit the tunneling rate is finite. An explicit formula is obtained in this case. A quantitative explanation without fitting parameter to a recent experiment is provided.

We show how two-dimensional incompressible quantum fluids and their excitations can be viewed as ${\mathit{W}}_{1+\mathrm{\infty }}$ edge conformal field theories, thereby providing an algebraic characterization of incompressibility. The Kac-Radul representation theory of the ${\mathit{W}}_{1+\mathrm{\infty }}$ algebra leads then to a purely algebraic complete classification of hierarchical quantum Hall states, which encompasses all measured fractions. Spin-polarized electrons in single-layer devices can only have Abelian anyon excitations.

An experimental analysis of the fractional quantum Hall effect is described in which oscillations in ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$ are treated as Shubnikov–de Haas oscillations of the composite fermions (CF) formed by a flux attachment transformation. We find a CF effective mass of 0.5${\mathit{m}}_{\mathit{e}}$ at zero effective field which increases weakly with effective magnetic field at a rate independent of carrier density. The CF quantum scattering times are the same as for the underlying single particle electron states.

The critical current ${\mathit{j}}_{\mathit{c}}$ and the pinning energy ${\mathit{U}}_{\mathit{c}}$ have been determined for three types of yttrium-based superconducting films from current ${\mathit{j}}_{\mathit{s}}$ and dynamic relaxation Q=d ln${\mathit{j}}_{\mathit{s}}$/d ln(dB/dt) data by means of the generalized inversion scheme. For B<2 T and T<80 K the temperature dependence of ${\mathit{j}}_{\mathit{c}}$ and ${\mathit{U}}_{\mathit{c}}$ for all films is found to be in excellent agreement with a model of single vortices pinned by randomly distributed weak pinning centers via spatial fluctuations of the charge carrier mean free path. Pinning due to spatial fluctuations of ${\mathit{T}}_{\mathit{c}}$ is not observed.

We report a sharp melting transition of the Bose glass in YBaCuO crystals with columnar defects installed by the irradiation with 1 GeV Au ions. The melting ${\mathit{B}}_{\mathrm{BG}}$(T) is tracked at low fields by the irreversibility line, which undergoes a remarkable abrupt crossover at a field ${\mathit{B}}_{\mathrm{cr}}$ for the vortices aligned with columns along the c axis. Below ${\mathit{B}}_{\mathrm{cr}}$, the upward curvature of ${\mathit{B}}_{\mathrm{BG}}$∝(1-T/${\mathit{T}}_{\mathit{c}}$${)}^{\mathrm{\alpha }}$ increases with the pin density (the exponent α grows from the clean value of ∼4/3 to ∼2 at the highest irradiation doses), in quantitative agreement with the theory of melting in the presence of correlated disorder. Above ${\mathit{B}}_{\mathrm{cr}}$, the linear in T irreversibility line is consistent with a transition into a (super)entangled vortex liquid.

A classical spin-one lattice gas model is used to study the competition between short-range ferromagnetic coupling and long-range antiferromagnetic Coulomb interactions. The model is a coarse-grained representation of frustrated phase separation in high-temperature superconductors. The ground states are determined for the complete range of parameters by using a combination of numerical and analytical techniques. The crossover between ferromagnetic and antiferromagnetic states proceeds via a rich structure of highly symmetric striped and checkerboard phases. There is no devil’s staircase behavior because mixtures of stripes with different period phase separate.

The magnetic a and c axes are switched by applying high magnetic field in ${\mathrm{DyCu}}_2$ single crystal. The virgin state has the Ising axis along the a direction with the two-step metamagnetism but the Ising axis is switched to the c direction by applying the field higher than 13 T along the c axis. The recovery of the virgin state is obtained either by increasing temperature above 100 K or applying the field higher than 5 T to the a axis. The switching cycle is quantitatively explained by the first order phase transition model.

The field dependence of the ground state of semi-infinite uniaxial antiferromagnets and films is investigated in terms of a two-dimensional area-preserving map, where the surfaces are introduced as appropriate boundary conditions. For the film, the ground state is calculated for any value of the number of planes in a very rapid and accurate way. For the semi-infinite system, we show that the so-called surface spin-flop state does not exist; by energetic arguments, we find that the instability of the antiferromagnetic configuration leads to an interchange of the sublattices. A nonhomogeneous ground state is instead found in the bulk spin-flop phase.

Periodic branched columns are observed for the first time in a layer of phase-separated magnetic colloid confined in a cell. The periodicity λ scales with the layer thickness L. In the thin limit, where no branching occurs, λ∝${\mathit{L}}^{1/2}$. In the thick limit, each column develops a tree structure with branches and roots, and the columns are separated by shrubs while the scaling relation crosses over to λ∝${\mathit{L}}^{2/3}$.

We present an analysis of the Korringa ratio in a dirty metal, emphasizing the case where a Stoner enhancement of the uniform susceptibility is present. We find that the relaxation rates are significantly enhanced by disorder, and that the inverse problem of determining the bare density of states from a study of the change of the Knight shift and relaxation rates with some parameter, such as pressure, has rather constrained solutions, with the disorder playing an important role. Some preliminary applications to the case of chemical substitution in the ${\mathrm{Rb}}_{3\mathrm{-}\mathit{x}}$${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{60}$ family of superconductors is presented and some other relevant systems are mentioned.

The optical conductivity of high quality decagonal quasicrystals of ${\mathrm{Al}}_{65}$${\mathrm{Co}}_{17}$${\mathrm{Cu}}_{18}$ and ${\mathrm{Al}}_{62}$${\mathrm{Co}}_{15}$${\mathrm{Cu}}_{20}$${\mathrm{Si}}_3$ shows a strong anisotropy between the periodic and the quasiperiodic directions. We suggest that this is due to the dramatic enhancement of scattering in the quasiperiodic planes. The analysis of the conductivity reveals a drastic difference between the electronic structure of the decagonal quasicrystals and the icosahedral quasicrystals.

We propose a new nonrelativistic Chern-Simons theory based on a simple modification of the standard Lagrangian. This admits asymptotically nonvanishing field configurations and is applicable to the description of systems of repulsive bosons. The new model supports topological vortices and has a self-dual limit, both in the pure Chern-Simons and in the mixed Chern-Simons-Maxwell cases. The analysis is based on a new formulation of the Chern-Simons theories as constrained Hamiltonian systems.

The mean area of two-dimensional unpressurized vesicles, or self-avoiding loops of fixed length N, behaves for large N as ${\mathit{A}}_0$${\mathit{N}}^{3/2}$, while their mean square radius of gyration behaves as ${\mathit{R}}_0^2$${\mathit{N}}^{3/2}$. The amplitude ratio ${\mathit{A}}_0$/${\mathit{R}}_0^2$ is computed exactly and found to equal 4π/5. The physics of the pressurized case, in both the inflated and collapsed phases, may be usefully related to that of a complex O(n) field theory coupled to a U(1) gauge field, in the limit n→0.

In certain two-dimensional models, collapsing matter forms a black hole if and only if the incoming energy flux exceeds the Hawking radiation rate. Near the critical threshold, the black hole mass is given by a universal formula in terms of the distance from criticality, and there exists a scaling solution describing the formation and evaporation of an arbitrarily small black hole.

A long-standing conjecture on the structure of renormalized, gauge invariant, integrated operators of arbitrary dimension in Yang-Mills theory is established. The general solution of the consistency condition for anomalies with sources included is also derived. This is achieved by computing explicitly the cohomology of the full unrestricted Becchi-Rouet-Stora-Tyutin operator in the space of local polynomial functionals with ghost number equal to zero or one. The argument does not use power counting and is purely cohomological. It relies crucially on standard properties of the antifeld formalism.

We examine the possibility of small CP-violating supersymmetry (SUSY) phases in string-inspired supergravity models in which supersymmetry is broken by the auxiliary components of the dilaton and moduli. It is found that the SUSY phases can be suppressed by a small factor governing the breakdown of the approximate Peccei-Quinn symmetries nonlinearly realized for the moduli superfields that participate in supersymmetry breaking. In many cases, the symmetry breaking factors are exponentially small for moderately large values of the moduli, leading to small phase values in a natural way.

A search for antiproton decay has been made at the Fermilab antiproton accumulator. Limits are placed on five antiproton decay modes. At the 95% C.L. we find that ${\mathrm{\tau }}_{\mathit{p}\mathrm{¯}}$/B(p¯→${\mathit{e}}^{\mathrm{-}}$γ)>1848 yr, ${\mathrm{\tau }}_{\mathit{p}\mathrm{¯}}$/B(p¯→${\mathit{e}}^0$${\mathrm{\pi }}^0$)>554 yr, ${\mathrm{\tau }}_{\mathit{p}\mathrm{¯}}$/B(p¯→${\mathit{e}}^{\mathrm{-}}$η)>171 yr,${\mathrm{\tau }}_{\mathit{p}\mathrm{¯}}$/B(p¯→${\mathit{e}}^{\mathrm{-}}$${\mathit{K}}_{\mathit{S}}^0$)>29 yr, and ${\mathrm{\tau }}_{\mathit{p}\mathrm{¯}}$/B(p¯→${\mathit{e}}^{\mathrm{-}}$${\mathit{K}}_{\mathit{L}}^0$)>9 yr.

We study chiral symmetry breaking in nuclear matter. For the dynamics we use a class of quark models with a chiral invariant confining potential. The mass gap equation is obtained when we minimize the energy of the matter with respect to the chiral angle φ and to the quark wave function in the nucleon. At low nuclear density ρ, we find that the chiral angle decreases slightly, the nucleon swells and the nucleon mass decreases. However, for the density of nuclear matter, we find that the chiral angle suffers an enhancement. We briefly discuss the physical consequences of this effect and its independence of the microscopic quark model.

Multifragmentation of the system α${+}^{197}$Au has been studied at incident energies of 1 and 3.6 GeV/nucleon with the new 4π setup, FASA. Mass, energy, and velocity of a few fragments are measured with high precision using time-of-flight telescopes, while for the other fragments, global multiplicity information is obtained from 55 CsI(Tl) detectors covering the main part of 4π. Very high mean IMF (intermediate mass fragment) multiplicities of 〈M${\mathrm{〉}}_{\mathrm{IMF}}$=5.1±0.8 are observed at the higher incident energy. Compared to the lower incident energy, they increase by 40%, indicating an increasing energy deposition with increasing incident energy.

We present data on hard-photon production in ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$${+}^{197}$Au and ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$${+}^{12}$C collisions at 95 MeV/nucleon. The photon source velocity ${\mathrm{\beta }}_{\mathit{S}}$ is investigated as a function of system size, photon energy, and impact parameter. In the heavy system, ${\mathrm{\beta }}_{\mathit{S}}$ is found to be sizably smaller than ${\mathrm{\beta }}_{\mathrm{beam}}$/2, except for very peripheral reactions. This unambiguously demonstrates that at intermediate bombarding energies photon emission is not solely dominated by first-chance p-n collisions, but carries also information on the later, stopping phase of the reaction.