Showing papers in "Physical Review Letters in 1987"
TL;DR: If a three-dimensionally periodic dielectric structure has an electromagnetic band gap which overlaps the electronic band edge, then spontaneous emission can be rigorously forbidden.
Abstract: It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling between matter and space, but that it can be controlled by modification of the properties of the radiation field. This is equally true in the solid state, where spontaneous emission plays a fundamental role in limiting the performance of semiconductor lasers, heterojunction bipolar transistors, and solar cells. If a three-dimensionally periodic dielectric structure has an electromagnetic band gap which overlaps the electronic band edge, then spontaneous emission can be rigorously forbidden.
12,787 citations
TL;DR: A new mechanism for strong Anderson localization of photons in carefully prepared disordered dielectric superlattices with an everywhere real positive dielectrics constant is described.
Abstract: A new mechanism for strong Anderson localization of photons in carefully prepared disordered dielectric superlattices with an everywhere real positive dielectric constant is described. In three dimensions, two photon mobility edges separate high- and low-frequency extended states from an intermediate-frequency pseudogap of localized states arising from remnant geometric Bragg resonances. Experimentally observable consequences are discussed.
9,067 citations
TL;DR: It is shown that dynamical systems with spatial degrees of freedom naturally evolve into a self-organized critical point, and flicker noise, or 1/f noise, can be identified with the dynamics of the critical state.
Abstract: We show that dynamical systems with spatial degrees of freedom naturally evolve into a self-organized critical point. Flicker noise, or 1/f noise, can be identified with the dynamics of the critical state. This picture also yields insight into the origin of fractal objects.
6,486 citations
TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations
TL;DR: A fourth-order interference technique has been used to measure the time intervals between two photons, and by implication the length of the photon wave packet, produced in the process of parametric down-conversion.
Abstract: A fourth-order interference technique has been used to measure the time intervals between two photons, and by implication the length of the photon wave packet, produced in the process of parametric down-conversion. The width of the time-interval distribution, which is largely determined by an interference filter, is found to be about 100 fs, with an accuracy that could, in principle, be less than 1 fs.
3,757 citations
TL;DR: The first experimental investigation of nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space, is reported.
Abstract: It was recently predicted that nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space. We report the first experimental investigation of these beams.
2,919 citations
TL;DR: A new approach to Monte Carlo simulations is presented, giving a highly efficient method of simulation for large systems near criticality, despite the fact that the algorithm violates dynamic universality at second-order phase transitions.
Abstract: A new approach to Monte Carlo simulations is presented, giving a highly efficient method of simulation for large systems near criticality. The algorithm violates dynamic universality at second-order phase transitions, producing unusually small values of the dynamical critical exponent.
2,443 citations
TL;DR: An error estimate is presented for this forecasting technique for chaotic data, and its effectiveness is demonstrated by applying it to several examples, including data from the Mackey-Glass delay differential equation, Rayleigh-Benard convection, and Taylor-Couette flow.
Abstract: We present a forecasting technique for chaotic data. After embedding a time series in a state space using delay coordinates, we ``learn'' the induced nonlinear mapping using local approximation. This allows us to make short-term predictions of the future behavior of a time series, using information based only on past values. We present an error estimate for this technique, and demonstrate its effectiveness by applying it to several examples, including data from the Mackey-Glass delay differential equation, Rayleigh-Benard convection, and Taylor-Couette flow.
1,836 citations
TL;DR: A new geometric phase factor is defined for any cyclic evolution of a quantum system, independent of the phase factor relating the initial and final state vectors and the Hamiltonian, for a given projection of the evolution on the projective space of rays of the Hilbert space.
Abstract: A new geometric phase factor is defined for any cyclic evolution of a quantum system. This is independent of the phase factor relating the initial and final state vectors and the Hamiltonian, for a given projection of the evolution on the projective space of rays of the Hilbert space. Some applications, including the Aharonov-Bohm effect, are considered. For the special case of adiabatic evolution, this phase factor is a gauge-invariant generalization of the one found by Berry.
1,819 citations
TL;DR: A valence-bond solid is presented, which is simply constructed out of valence bonds, is nondegenerate, and breaks no symmetries, and there is an energy gap and an exponentially decaying correlation function.
Abstract: We present rigorous results on a phase in antiferromagnets in one dimension and more, which we call a valence-bond solid. The ground state is simply constructed out of valence bonds, is nondegenerate, and breaks no symmetries. There is an energy gap and an exponentially decaying correlation function. Physical applications are mentioned.
1,550 citations
IBM1
TL;DR: Using an atomic force microscope, atomic-scale features on the frictional force acting on a tungsten wire tip sliding on the basal plane of a graphite surface at low loads are observed.
Abstract: Using an atomic force microscope, we have observed atomic-scale features on the frictional force acting on a tungsten wire tip sliding on the basal plane of a graphite surface at low loads, < 10-4 N. The atomic features have the periodicity of the graphite surface and are discussed in terms of a phenomenological model for the tip motion described by the sum of a periodic tip-surface force and the spring force exerted by the wire.
TL;DR: Proposition d'une nouvelle methode, basee sur the theorie des perturbations dans laquelle la reponse au potentiel total est obtenue par iteration jusqu'a l'autocoherence, la sommation sur les bandes de conduction evitee grâce a une technique a fonction de Green.
Abstract: We present a new scheme to study the linear response of crystals which combines the advantages of the dielectric-matrix and supercell (``direct'') approaches yet avoids many of their drawbacks. The numerical complexity of the algorithm is of the same order as that of a self-consistent calculation for the unperturbed system. The method is not restricted to local perturbations as the dielectric-matrix one nor to short wavelengths as the direct one. As an application, we calculate the long-wavelength optical phonons in Si and GaAs, both transverse and longitudinal, using norm-conserving pseudopotentials, and without any use of supercells.
TL;DR: In this article, it was shown that the properties of high-mathrm{T}$ oxide superconductors are consistent with a model in which the charge carriers are holes in the O(2p) states and the pairing is mediated by strong coupling to local spin configurations on the Cu sites.
Abstract: It is shown that the properties of high-${\mathrm{T}}_{\mathrm{c}}$ oxide superconductors are consistent with a model in which the charge carriers are holes in the O(2p) states and the pairing is mediated by strong coupling to local spin configurations on the Cu sites.
TL;DR: A neutrino burst was observed in the Kamiokande II detector on 23 February, 7:35:35 UT (7.1 min) during a time interval of 13 sec as mentioned in this paper.
Abstract: A neutrino burst was observed in the Kamiokande II detector on 23 February, 7:35:35 UT (\ifmmode\pm\else\textpm\fi{}1 min) during a time interval of 13 sec. The signal consisted of 11 electron events of energy 7.5 to 36 MeV, of which the first two point back to the Large Magellanic Cloud with angles 18\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}18\ifmmode^\circ\else\textdegree\fi{} and 15\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}27\ifmmode^\circ\else\textdegree\fi{}.
TL;DR: The confinement and cooling of an optically dense cloud of neutral sodium atoms by radiation pressure was reported, provided by three retroreflected laser beams propagating along orthogonal axes, with a weak magnetic field used to distinguish between the beams.
Abstract: We report the confinement and cooling of an optically dense cloud of neutral sodium atoms by radiation pressure. The trapping and damping forces were provided by three retroreflected laser beams propagating along orthogonal axes, with a weak magnetic field used to distinguish between the beams. We have trapped as many as ${10}^{7}$ atoms for 2 min at densities exceeding ${10}^{11}$ atoms ${\mathrm{cm}}^{\ensuremath{-}3}$. The trap was \ensuremath{\simeq}0.4 K deep and the atoms, once trapped, were cooled to less than a millikelvin and compacted into a region less than 0.5 mm in diameter.
TL;DR: A burst of eight neutrino events preceding the optical detection of the supernova in the Large Magellanic cloud has been observed in a large underground water Cherenkov detector.
Abstract: A burst of eight neutrino events a preceding the optical detection of the supernova in the Large Magellanic Cloud has been observed in a large underground water Cherenkov detector. The events span an interval of 6 s and have visible energies in the range 20-40 MeV.
TL;DR: Observation de la transition supraconductrice a 91 K, sur 1,5 K and determination of the densite de courant critique, de l'effet Meissner, du champ critique, du parametre de Sommerfeld, de parametres GL.
Abstract: We have prepared and identified as a single phase the high-temperature superconducting compound in the chemical system Y-Ba-Cu-O, an orthorhombic, distorted oxygen-deficient perovskite of stoichiometry ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{9\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (\ensuremath{\delta}\ensuremath{\simeq}2.1). Samples exhibit zero resistance at 91 K, with a transition width of 1.5 K. The Meissner effect attains a value of 76% of the independently measured diamagnetic susceptibility. We estimate parameters that characterize this superconductor, e.g., \ensuremath{\gamma}\ensuremath{\simeq}3--5 mJ (mole Cu${)}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{K}}^{\mathrm{\ensuremath{-}}2}$. The critical current density at 77 K and H=0 exceeds 1100 A/${\mathrm{cm}}^{2}$.
TL;DR: Unusual structure and large electric-field--induced oscillations have been observed in the current-voltage curves of small-area tunnel junctions arranged in a low-capacitance multiple-junction configuration.
Abstract: Unusual structure and large electric-field--induced oscillations have been observed in the current-voltage curves of small-area tunnel junctions arranged in a low-capacitance (\ensuremath{\lesssim}1 fF) multiple-junction configuration. This behavior arises from the tunneling of individual electrons charging and discharging the capacitance. The observations are in accord with what would be expected from a simple model of the charging energies and voltage fluctuations of e/C associated with such effects.
TL;DR: The dynamics of the interaction of a single Rydberg atom with a single mode of an electromagnetic field in a superconducting cavity was investigated and the quantum collapse and revival predicted by the Jaynes-Cummings model were demonstrated experimentally for the first time.
Abstract: The dynamics of the interaction of a single Rydberg atom with a single mode of an electromagnetic field in a superconducting cavity was investigated. Velocity-selected atoms were used and the evolution of the atomic inversion as atom and field exchange energy was observed. The quantum collapse and revival predicted by the Jaynes-Cummings model were demonstrated experimentally for the first time. The evaluation of the dynamic behavior of the atoms allows us to determine the statistics of the few photons in the cavity.
TL;DR: It is argued here that in universes that do not recollapse, the only bound on the cosmological constantlambda is that it should not be so large as to prevent the formation of gravitationally bound states, and it turns out that the bound is quite large.
Abstract: In recent cosmological models, there is an "anthropic" upper bound on the cosmological constant $\ensuremath{\Lambda}$. It is argued here that in universes that do not recollapse, the only such bound on $\ensuremath{\Lambda}$ is that it should not be so large as to prevent the formation of gravitationally bound states. It turns out that the bound is quite large. A cosmological constant that is within 1 or 2 orders of magnitude of its upper bound would help with the missing-mass and age problems, but may be ruled out by galaxy number counts. If so, we may conclude that anthropic considerations do not explain the smallness of the cosmological constant.
TL;DR: An apparent superconducting transition with an onset temperature above 40 K has been detected under pressures in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La/sub 2/O/ sub 3/, CuO, and BaCO/sub 3/ followed by a decomposition of the mixture in a reduced atmosphere.
Abstract: An apparent superconducting transition with an onset temperature above 40 K has been detected under pressure in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La2O3, CuO, and BaCO3 followed by a decomposition of the mixture in a reduced atmosphere. The experiment is described and the results of effects of magnetic field and pressure are discussed.
TL;DR: It is proposed that space-time at the smallest scales is in reality a causal set: a locally finite set of elements endowed with a partial order corresponding to the macroscopic relation that defines past and future.
Abstract: We propose that space-time at the smallest scales is in reality a causal set: a locally finite set of elements endowed with a partial order corresponding to the macroscopic relation that defines past and future. We explore how a Lorentzian manifold can approximate a causal set, noting in particular that the thereby defined effective dimensionality of a given causal set can vary with length scale. Finally, we speculate briefly on the quantum dynamics of causal sets, indicating why an appropriate choice of action can reproduce general relativity in the classical limit.
TL;DR: In the extended absorption region up to 200 eV above the Fermi level a small spin-dependent absorption is observed and thus is expected to give information on the magnetic neighborhood of the absorbing atom.
Abstract: The transmission of synchrotron radiation through magnetized iron at energies above the K-absorption edge shows relative differences for right and left circular polarization of several times ${10}^{\mathrm{\ensuremath{-}}4}$. The observed spin dependence of the near-edge photoabsorption is proportional to the difference of the spin densities of the unoccupied bands. In the extended absorption region up to 200 eV above the Fermi level a small spin-dependent absorption is observed and thus is expected to give information on the magnetic neighborhood of the absorbing atom.
TL;DR: An adaptive neural network with asymmetric connections is introduced that bears a resemblance to the master/slave network of Lapedes and Farber but it is architecturally simpler.
Abstract: An adaptive neural network with asymmetric connections is introduced. This network is related to the Hopfield network with graded neurons and uses a recurrent generalization of the \ensuremath{\delta} rule of Rumelhart, Hinton, and Williams to modify adaptively the synaptic weights. The new network bears a resemblance to the master/slave network of Lapedes and Farber but it is architecturally simpler.
TL;DR: Under suitable conditions, diffraction gives rise to an instability which leads to the emergence of a stationary spatial dissipative structure in the transverse profile of the transmitted beam.
Abstract: We consider a nonlinear, passive optical system contained in an appropriate cavity, and driven by a coherent, plane-wave, stationary beam. Under suitable conditions, diffraction gives rise to an instability which leads to the emergence of a stationary spatial dissipative structure in the transverse profile of the transmitted beam.
TL;DR: In this article, the electron-phonon interaction causes temperature relaxation for metal superconductivity, which is shown to be rapid for a metal metal when the metal is heated to a temperature greater than the lattice temperature.
Abstract: If electrons in a metal are heated to a temperature ${\mathrm{T}}_{\mathrm{e}}$ greater than the lattice temperature ${\mathrm{T}}_{\mathrm{L}}$, the electron-phonon interaction causes temperature relaxation ${\mathrm{dT}}_{\mathrm{e}}$/dt=${\ensuremath{\gamma}}_{\mathrm{T}}$(${\mathrm{T}}_{\mathrm{L}}$-${\mathrm{T}}_{\mathrm{e}}$) which is rapid for ${\mathrm{T}}_{\mathrm{L}}$g${\mathrm{\ensuremath{\theta}}}_{\mathrm{D}}$. A formula ${\ensuremath{\gamma}}_{\mathrm{T}}$=3\ensuremath{\Elzxh}\ensuremath{\lambda}〈${\mathrm{\ensuremath{\omega}}}^{2}$〉/\ensuremath{\pi}${\mathrm{k}}_{\mathrm{B}{\mathrm{T}}_{\mathrm{e}}}$ is derived, where \ensuremath{\lambda}〈${\mathrm{\ensuremath{\omega}}}^{2}$〉=\ensuremath{\eta}/M is an important parameter in the theory of superconductivity. Quantitative agreement with recent experiments is good.
IBM1
TL;DR: In this article, the diamagnetism observed in the zero-field--cooled state is considerably larger than under field cooling, indicating the existence of a superconductive glass state.
Abstract: Susceptibility and magnetic-moment measurements from 1.9 to 35 K in magnetic fields up to 1.5 T in powder samples of La/sub 2/CuO/sub 4-//sub y/:Ba are reported. The diamagnetism observed in the zero-field--cooled state is considerably larger than under field cooling. The former is metastable like the magnetic moment induced after switching the field off. These observations indicate the existence of a superconductive glass state.
TL;DR: When an intense electromagnetic wave is incident obliquely on a sharply bounded overdense plasma, strong energy absorption can be accounted for by the electrons that are dragged into the vacuum and sent back into the plasma with velocities vapprox.
Abstract: When an intense electromagnetic wave is incident obliquely on a sharply bounded overdense plasma, strong energy absorption can be accounted for by the electrons that are dragged into the vacuum and sent back into the plasma with velocities v\ensuremath{\simeq}${v}_{\mathrm{osc}}$. This mechanism is more efficient than usual resonant absorption for ${v}_{\mathrm{osc}/\mathrm{\ensuremath{\omega}}g\mathrm{L}}$, with L being the density gradient length. In the very high-intensity ${\mathrm{CO}}_{2}$-laser--target interaction, this mechanism may account for most of the energy absorption.
TL;DR: In this paper, a simple model for the energy cascading process in the inertial range is presented that fits remarkably well the entire spectrum of scaling exponents for the dissipation field in fully developed turbulence.
Abstract: A simple model is presented for the energy-cascading process in the inertial range that fits remarkably well the entire spectrum of scaling exponents for the dissipation field in fully developed turbulence. The scheme is a special case of weighted curdling and its one-dimensional version is a simple generalized two-scale Cantor set with equal scales but unequal weights (with ratio\ensuremath{\sim}(7/3). This set displays all the measured multifractal properties of one-dimensional sections of the dissipation field.
TL;DR: The fundamental relationship between radiative lifetime and spectral linewidth of freeexcitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.
Abstract: The fundamental relationship between radiative lifetime and spectral linewidth of free excitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.