By using the prototypical ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As/GaAs system, we demonstrate the unique capability of scanning tunneling microscopy to directly map out detailed electronic structure across heterojunctions. Three novel applications are reported: (1) precise determination of band offsets, (2) measurement of asymmetrical electronic transition widths between the normal and inverted interfaces, and (3) mapping of multiple-valley band structures. Important implications of these results are discussed.

Impurity scatterers, particularly in the unitary limit, produce low energy quasiparticles in a two-dimensional d-wave superconductor. We argue that even if the impurity concentration is small so that the wave functions in the normal state are essentially extended, the quasiparticles in the superconducting state become strongly localized for a short coherence length d-wave superconductor. An effective mobility gap then leads to thermally activated behavior for the microwave conductivity and possibly for the London penetration depth. We argue that this observation allows some puzzling data on oxide superconductors to be reconciled with the hypothesis of d-wave pairing.

The spin-lattice relaxation rate W on ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$ has been measured in the mixed state of a ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CuO}}_6$ aligned powder sample with ${\mathit{T}}_{\mathit{c}}$=100 K. At T<25 K, W∝T and decreases with increasing magnetic field. This behavior is explained as caused by fluctuations of pancake vortices; the latter induce a time dependent random magnetic field which causes the relaxation of nuclear spins.

We have performed simultaneous measurements of magnetic relaxation and the accompanying power dissipation in a number of BiSrCaCuO crystals at temperatures between 0.5 and 4.2 K. The nonvanishing relaxation rate in bulk superconductors at low temperatures, recently discussed as evidence of a quantum tunneling of vortices, is argued to be governed by self-heating of the superconductor by moving vortices.

The irreversibility line ${\mathit{B}}_{\mathit{m}}$(T) of monocrystalline superconducting ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ has been measured in magnetic fields H parallel to the c axis of the crystal. For low inductions B near ${\mathit{T}}_{\mathit{c}}$, we find a parabolic temperature dependence, ${\mathit{B}}_{\mathit{m}}$≊${\mathit{B}}_0$(${\mathit{T}}_{\mathit{c}}$/T-1${)}^2$, while for larger inductions, ${\mathit{B}}_{\mathit{m}}$ grows exponentially with ${\mathit{T}}^{\mathrm{-}1}$. We argue that the two regimes reflect the three- and the quasi-two-dimensional character of the respective vortex fluctuations. In both regimes, a Lindemann-type melting criterion yields quantitative expressions for ${\mathit{B}}_{\mathit{m}}$(T) which reproduce the experimental data very well.

The relationship between the low temperature orthorhombic-tetragonal (OT) phase transition in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_4$ and the suppression of the superconducting state in samples with x=0.125 has been investigated. Using high resolution synchrotron x-ray diffraction we show that the phase composition of a superconducting x=0.15 sample varies with temperature identically to an x=0.125 sample. This shows that the tetragonal structure does support bulk superconductivity in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_4$ and the electronic transition which suppresses superconductivity at x=0.125 is distinct from the OT structural transition.

We present the results of differential resistance (dV/dI) measurement on high-transmittance Nb-Ag (or Al) microjunctions. At low bias, dV/dI has the conventional Blonder-Tinkham-Klapwijk double-dip structure plus a sharp single dip at zero bias. This zero-bias anomaly is completely suppressed by a modification in interface. It is insensitive to magnetic field. We relate it to the electron phase-coherence effect in the proximity of superconducting gap potential Δ. Above Δ/e, dV/dI exhibits an anomalous peak, whose position is found to be proportional to Δ(T,H).

A three-dimensional lattice of Heisenberg spins with nearest-neighbor interactions is studied by numerical simulation under the constraint that no free topological singularities (hedgehogs) are allowed. Only nearest-neighbor pairs of oppositely charged hedgehogs are permitted in the sum over configurations. A disordering transition with exponents different from the usual Heisenberg transition is found and tentatively identified as a pure spin wave disordering transition.

In order to provide a numerical criterion for superconductivity, the ground state energy ${\mathit{E}}_0$(Φ) is calculated for the attractive and repulsive Hubbard models on a cylinder geometry threaded by a flux Φ. From the functional form of ${\mathit{E}}_0$(Φ), superconducting ground states may be identified without prior knowledge of the pairing symmetry. ${\mathit{E}}_0$(Φ) is calculated with Monte Carlo methods. For the attractive Hubbard model, our results confirm the existence of a superconducting ground state. In contrast, our results show that the quarter-filled repulsive Hubbard model is not superconducting and that a Hartree-Fock paramagnetic approximation fits the data very well.

${\mathrm{LiHo}}_{0.167}$${\mathrm{Y}}_{0.833}$${\mathrm{F}}_4$ is a dilute dipolar-coupled Ising magnet with a spin glass transition which can be crossed with temperature T (${\mathit{T}}_{\mathit{g}}$=0.13 K) or with an effective transverse field Γ(${\mathrm{\Gamma }}_{\mathit{g}}$=1 K at T=0). The nonlinear susceptibility contains a diverging component which dominates at T=98 mK, but disappears by 25 mK. At the same time, the onset of spin glass behavior in the dissipative linear susceptibility becomes sharper. We conclude that, contrary to theoretical expectations, quantum transitions can be qualitatively different from thermally driven transitions in real spin glasses.

We determined oscillatory periods, phases, and coupling strengths for [001] Fe/V and Fe/Cr, using a highly accurate, non-self-consistent first-principles method. The periods obtained for Fe/Cr are consistent with experiment both for paramagnetic and antiferromagnetic Cr. These results clearly show how the Cr antiferromagnetism affects the exchange coupling. For [001] Fe/V, we predict short and long periods that have not yet been observed, but provide tests for the theory. We also discuss the merits of our computational approach.

A Korringa-Kohn-Rostoker Green’s function method for planar perturbations and a frozen potential method are used to evaluate the interaction energies of Fe and Co monolayers in Cu separated by up to 23 spacer layers. For the [100] orientation a phase shift of π is obtained between the Fe and Co oscillations and the three antiferromagnetic peaks observed experimentally are well described. For [110] an interesting beat effect is obtained leading to very different results for the Fe and Co layers.

Optical second harmonic generation (SHG) in 75° reflection was studied on longitudinally magnetized PtMnSb(111) and magnetic circular dichroism was observed with SHG. For circularly polarized incident light of 532 nm it amounts to (7±1)%. For linearly polarized incident radiation this leads to a nonlinear magneto-optical Kerr rotation of (14±2)°. The strong symmetry-breaking effect of the magnetization is demonstrated by a 90° turn of the SH polarization ellipse with regard to the linear polarization of the fundamental light.

Time-resolved Raman scattering measurements are made by using 110 fs laser pulses in germanium at the initial carrier density of 3×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Intensity build-up is clearly observed for the Raman scattering due to photoexcited electrons in L valleys and is quantitatively analyzed in terms of the theory on the electronic light scattering from a multicomponent electron gas. We show that photoexcited electrons initially created in the Γ valley are scattered into L valleys with a time constant of 1.2±0.1 ps.

${\mathrm{Xe}}^{\mathit{q}+}$ ions with charge up to q=33 and energies 3.7q keV are scattered under a grazing angle of incidence from a clean and flat Al(111) surface. Because of the image charge interaction the ions are accelerated on the incident path towards the surface plane which results in increased effective angles of incidence for the scattered projectiles. From the angular distributions for reflected neutralized projectiles we deduce the image charge interaction energies gained by the incident ions in front of the surface. Our data are in fair agreement with a ${\mathit{q}}^{3/2}$ dependence for the image energies as predicted from a simple classical overbarrier model.

Total low-energy electron yields for the normal incidence interaction of slow, very highly charged ions ${(}^{136}$${\mathrm{Xe}}^{\mathit{q}+}$, 21≤q≤51; ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}_{}^{\mathit{q}+}{}_{}{}^{}$, 51≤q≤80) with a clean gold surface have been determined from the related measured electron emission statistics. The projectile impact energies could be reduced down to the image charge acceleration limit. The electron emission yield was found to increase proportionally with the increasing projectile charge state in all cases studied, suggesting no saturation in the ability of the Au target to provide necessary electrons within the above surface interaction time (e.g., about 280 electrons/projectile for ${\mathrm{Th}}^{79+}$ in less than ${10}^{\mathrm{-}13}$ s). Because of the relatively narrow energy distribution of the incident ions, as well as their very high charge states, the first clear measurements of the image charge acceleration from electron emission yields could be performed. Results of a quantitative study of this acceleration are in good agreement with those of a theoretical model based on classical over the barrier transitions (recently developed by J. Burgdörfer et al.).

We report precise measurements of the time correlation function in a pseudo two-component water-in-oil microemulsion system made of surfactant AOT, water, and decane close to its consolute critical point and percolation threshold. Systematic studies of the intensity correlation functions using a correlator with a logarithmic sampling time show sizable deviations from a single exponential decay. It is shown that an extension of the dynamic droplet model is able to account for the nonexponential behavior at intermediate and long times. The linewidth is in satisfactory agreement with the model, which also takes into account the finite size of the microemulsion droplets.

Assuming that air-sea interaction is the primary energy source of the hurricane, we suggest that a new class of resonantly forced internal solitary waves protects the fuel of the storm by preventing or reducing entrainment.

We derive a new completely integrable dispersive shallow water equation that is bi-Hamiltonian and thus possesses an infinite number of conservation laws in involution. The equation is obtained by using an asymptotic expansion directly in the Hamiltonian for Euler’s equations in the shallow water regime. The soliton solution for this equation has a limiting form that has a discontinuity in the first derivative at its peak.

It is shown that it is possible to demonstrate nonlocality for two particles without using inequalities for all entangled states except maximally entangled states such as the singlet state. The eigenvectors corresponding to the measurements that must be performed to do this are exhibited and found to have a particularly simple relationship to the entangled state.