We find that slow electrons moving in a vacuum near the surface of a polar dielectric or semiconductor most probably will be trapped in the Rydberg states localized in a one-dimensional image potential near the surface. The trapping is due to the inelastic scattering of electrons from the surface polarization modes. The probability of inelastic scattering of electrons into the Rydberg states increases anomalously with a decrease in the energy of the electrons.

We study nonequilibrium edge state transport in the fractional quantum Hall regime at filling g=1/m. Tunneling of Laughlin quasiparticles between edges is shown to generate both current and voltage shot noise with a universal ratio of noise amplitudes given by (${ge}^2$/h${)}^2$. In the weak backscattering limit we predict a current shot noise satisfying Poisson statistics with charge ge, which should enable a direct measurement of the fractional charge of the quasiparticle. On resonance the quasiparticles tunnel in pairs and the effective charge entering the current shot noise becomes 2ge.

The ν=1 quantum Hall effect in bilayer 2D electron systems is shown to continuously evolve from a regime dominated by single-particle tunneling into one where interlayer Coulomb interactions stabilize the state. This many-body integer quantum Hall state exhibits a phase transition to a compressible state at large layer separation. We also find evidence for an intriguing and unexpected second transition to a new incompressible state, driven by an in-plane magnetic field. While the origin of this last result is unclear, we discuss a recent model of a pseudospin textural phase transition.

Double-layer quantum Hall systems have interesting properties associated with interlayer correlations. At ν=1/m where m is an odd integer they exhibit spontaneous symmetry breaking equivalent to that of spin 1/2 easy-plane ferromagents, with the layer degree of freedom playing the role of spin. We explore the rich variety of quantum and finite temperature phase transitions in these systems. In particular, we show that a magnetic field oriented parallel to the layers induces a highly collective commensurate-incommensurate phase transition in the magnetic order.

Time-resolved magnetoluminescence was used to study the hierarchy of the fractional quantum Hall effect (FQHE) states. Several different families of the FQHE states are observed. A striking symmetry in the dependence of the chemical potential discontinuity on the filling factor is found inside all families of the FQHE states.

We have observed two forms of scaling in magnetotransport properties of (111) Co/Cu superlattices: (1) the extraoridnary Hall coefficient ${\mathit{R}}_{\mathit{s}}$ correlates with the resistivity ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$(0) in the form ${\mathit{R}}_{\mathit{s}}$∼${\mathrm{\rho }}_{\mathit{x}\mathit{x}}^2$(0), and (2) the magnetothermopower S(H) correlates with the magnetoresistivity ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$(H) in the form S(H)/T∼${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$(0)/${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$(H). The first effect relates to quantum mechanical side jump while the other relates to interfacial spin-dependent density of states (DOS). These results revel the different roles of bulklike spin-dependent scattering in Co layers and spin-dependent DOS of interfacial layers in causing the observed large positive extraodinary Hall effect and giant longitudinal magnetotransport.

We report muon-spin-rotation (μSR) measurements of the a-b magnetic penetration depth (${\lambda }_{\mathit{a}\mathit{b}}$) in the vortex state of high quality single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.95}$. Contrary to earlier μSR studies on powders and crystal mosaics, 1/${\lambda }_{\mathit{a}\mathit{b}}^2$ shows a strong linear temperature dependence below 50 K which weakens with increasing magnetic field. These results support recent microwave cavity measurements in zero field and provide further evidence for unconventional pairing of carriers.

Magnetic decoration has been used to investigate the role of surface pinning on the flux-line lattice (FLL) of high-quality ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ single crystals. We find that surface steps pin flux lines at the sample surface, and that strong pinning along large steps creates grain boundaries (GBs) in the FLL. Analysis of the competing energetics of pinning versus GB formation leads to a criteria for the formation of extended GBs, and also indicates that these GBs penetrate through the entire sample. Surface pinning, which should occur in all real samples, will thus significantly affect the bulk FLL structure in these materials.

The equilibrium resistive transition of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ epitaxial films was measured at high pulsed current densities J, to promote homogeneous current flow and free flux flow. The superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ was then depressed as a function of J in fixed fields H. The shifts in ${\mathit{T}}_{\mathit{c}}$, defined near midtransition, scaled following Ginzburg-Landau behavior: Δ${\mathit{T}}_{\mathit{c}}$(H,J)/${\mathit{T}}_{\mathit{c}}$(H,0)=[J/${\mathit{J}}_0$${]}^{2/3}$, where ${\mathit{J}}_0$ is a field- and current-indpendent constant.

We measure the specific heat C under pressure of high purity polycrystals of the heavy fermion supeconductor ${\mathrm{U}}_{0.978}$${\mathrm{Th}}_{0.022}$${\mathrm{Be}}_{13}$ with a pressure resolution equivalent to 0.0002 in Th concentration. We discover a new low temperature phase boundary independent of temperature and close to the critical pressure required to merge the two transitions observed in C(T).

Zero-field ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ nuclear quadrupole resonance (NQR) has been used to characterize the antiferromagnetic transition in nearly stoichiometric single crystals of ${\mathrm{La}}_2$${\mathrm{CuO}}_{4+\mathrm{\delta }}$ (Néel temperatures ${\mathit{T}}_{\mathit{N}}$ between 275 and 318 K). The onset of the NQR Zeeman splitting at ${\mathit{T}}_{\mathit{N}}$ is abrupt but continuous, indicative of a second-order phase transition with either a crossover in critical behavior just below ${\mathit{T}}_{\mathit{N}}$ or a very small critical exponent β≲0.1. The absence of any anomaly at ${\mathit{T}}_{\mathit{N}}$ in the ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ electric field gradient indicates no accompanying structural distortion.

A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness has been observed in an epitaxial fcc (001) triple wedge sample containing two Co wedges and one Cu wedge. Our result is consistent with an oscillation period of 6–7 Å Co—a value that agrees with the period of 3.5 monolayers of Co derived from the extremal wave vector that spans the ellipsoidal hole pocket centered at the X point of the fcc Co spin-down Fermi surface. This shows that the interlayer exchange coupling does not just involve an interaction localized at the interfaces, but is a property of the sandwich as a whole.

Evidence of the existence and distribution of an induced spin polarization of the conduction electrons in the Cu layers of Fe/Cu multilayers has been obtained by nuclear magnetic-resonance (NMR). Fine structure associated with the spin-echo signal of ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ and ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ nuclei shows that the spin polarization and an associated exchange field oscillate in sign, similar to the characteristics of the RKKY interaction. However, an accurate determination of the period of the oscillations cannot be determined solely from the NMR data at the present time.

The macroscopic quantum tunneling of a planar domain wall in a ferromagnetic metal is studied based on the Hubbard model. It is found that the Ohmic dissipation is present even at zero temperature due to the gapless Stoner excitation, which is the crucial difference from the case of the insulating magnet. The dissipative effect is calculated as a function of the width of the wall and is shown to be effective in a thin wall and in a weak ferromagnet. The results are discussed in the light of recent experiments on ferromagnets with strong anisotropy.

We use time resolved four wave mixing to study electron scattering in modulation doped GaAs quantum wells in high magnetic fields up to 8 T. We find a decrease in scattering rates relative to the zero field behavior. The four wave mixing signal shows a strong enhancement at the lowest Landau level which we attribute to the Fermi edge singularity.

We consider the focusing and deflection of a nonresonant atomic beam propagating through a spatially inhomogeneous quantized electromagnetic field. Different Fock states of the field deflect the atoms in different angles and focus them at different points. We find a regime in which individual foci corresponding to neighboring Fock states can be reoslved even for large average number of photons. In this sense this quantum lens for atomic waves leaves intact the discreteness of the photons even in the classical limit.

A new continuum model for hard-core fermions with ν colors is presented and solved exactly in arbitrary dimensions. The model has the SU(ν,1) supersymmetry in an exchange interaction and a kinetic-energy part. Through a renormalization to regularize operator products at short distances, free SU(ν) fermions emerge as eigenstates of the model. This corresponds to a nonrelativistic and supersymmetric version of the equivalence of SU(ν)×SU(ν) Wess-Zumino-Witten Lagrangian to free relativistic fermions.

A quantum Hamiltonian which evolves the gravitational field according to time as measured by constant surfaces of a scalar field is defined through a regularization procedure based on the loop representation, and is shown to be finite and diffeomorphism invariant. The problem of constructing this Hamiltonian is reduced to a combinatorial and algebraic problem which involves the rearrangements of lines through the vertices of arbitrary graphs. This procedure also provides a construction of the Hamiltonian constraint as a finite operator on the space of diffeomorphism invariant states as well as a construction of the operator corresponding to the spatial volume of the Universe.

Two types of self-gravitating particle solutions found in several theories with non-Abelian fields are smoothly connected by a family of nontrivial black holes. There exists a maximum point of the black hole entropy where the stability of solutions changes. This criterion is universal, and the changes in stability follow from a catastrophe-theoretic analysis of the potential function defined by black hole entropy.

According to recent reports there is an excess correlation and an apparent regularity in the galaxy one-dimensional polar distribution with a characteristic scale of 128${\mathit{h}}^{\mathrm{-}1}$ Mpc. This apparent spatial periodicity can be naturally explained by a time oscillation of the gravitational constant G. On the other hand, periodic growth features of bivalve and coral fossils appear to show a periodic component in the time dependence of the number of days per year. We show that a time oscillating gravitational constant with similar period and amplitude can explain such a feature.