Showing papers in "Physical Review Letters in 1988"
TL;DR: This work ascribes this giant magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecularbeam epitaxy to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.
Abstract: We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecularbeam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with ${t}_{\mathrm{Cr}}=9$ \AA{}, at $T=4.2$ K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.
7,993 citations
TL;DR: A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance in the absence of an external magnetic field, and exhibits the so-called "parity anomaly" of (2+1)-dimensional field theories.
Abstract: A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance ${\ensuremath{\sigma}}^{\mathrm{xy}}$ in the absence of an external magnetic field. Massless fermions without spectral doubling occur at critical values of the model parameters, and exhibit the so-called "parity anomaly" of (2+1)-dimensional field theories.
4,606 citations
TL;DR: The first expenmental study of the resistance of ballistic pomt contacts m the 2DEG of high-mobihty GaAs-AlGaAs heterostructures is reported.
Abstract: As a result of the high mobihty attamable in the twodimensional electron gas (2DEG) in GaAs-AlGaAs heterostructures it is now becoming feasible to study ballistic transport in small devices '"6 In metals ideal tools for such studies are constnctions havng a width W and length L much smaller than the mean free path le These are known as Sharvin pomt contacts 7 Because of the ballistic transport through these constnctions, the resistance is determmed by the pomt-contact geometry only Point contacts have been used extensively for the study of elastic and melastic electron scattermg With use of biased pomt contacts, electrons can be mjected mto metals at energies above the Fermi level This allows the study of the energy dependence of the scattermg mechamsms 8 With the use of a geometry containmg two pomt contacts, with Separation smaller than le, electrons mjected by a pomt contact can be focused mto the other contact, by the application of a magnetic field This technique (transverse electron focusmg) has been applied to the detailed study of Fermi surfaces 9 In this Letter we report the first expenmental study of the resistance of ballistic pomt contacts m the 2DEG of high-mobihty GaAs-AlGaAs heterostructures The smgle-pomt contacts discussed m this paper are part of a double-pomt-contact device The results of transverse electron focusmg m these devices will be published elsewhere '° The pomt contacts are dehned by electrostatic depletion of the 2DEG underneath a gate This method, which has been used by several authors for the study of l D conduction,'1 offers the possibility to control the width of the pomt contact by the gate voltage Control of the width is not feasible in metal pomt contacts
2,508 citations
TL;DR: It is found that the usual measuring procedure for preselected and postselected ensembles of quantum systems gives unusual results and under some natural conditions of weakness of the measurement, its result consistently defines a new kind of value for a quantum variable, which is called the weak value.
Abstract: We have found that the usual measuring procedure for preselected and postselected ensembles of quantum systems gives unusual results. Under some natural conditions of weakness of the measurement, its result consistently defines a new kind of value for a quantum variable, which we call the weak value. A description of the measurement of the weak value of a component of a spin for an ensemble of preselected and postselected spin-(1/2 particles is presented.
2,224 citations
TL;DR: In this paper, a new method for using the data from Monte Carlo simulations that can increase the efficiency by 2 or more orders of magnitude is presented. But the method is not applicable to statistical models and lattice-gauge theories.
Abstract: We present a new method for using the data from Monte Carlo simulations that can increase the efficiency by 2 or more orders of magnitude. A single Monte Carlo simulation is sufficient to obtain complete thermodynamic information over the entire scaling region near a phase transition. The accuracy of the method is demonstrated by comparison with exact results for the d=2 Ising model. New results for d=2 eight-state Potts model are also presented. The method is generally applicable to statistical models and lattice-gauge theories.
2,219 citations
TL;DR: On discute d'une technique alternative aux automates des gaz sur reseau pour etudier des proprietes hydrodynamiques, a savoir la modelisation d'un gaz reticulaire a l'aide d’une equation de Boltzman.
Abstract: We discuss an alternative technique to the lattice-gas automata for the study of hydrodynamic properties, namely, we propose to model the lattice gas with a Boltzmann equation. This approach completely eliminates the statistical noise that plagues the usual lattice-gas simulations and therefore permits simulations that demand much less computer time. It is estimated to be more efficient than the lattice-gas automata for intermediate to low Reynolds number $R\ensuremath{\lesssim}100$.
1,898 citations
IBM1
TL;DR: An empirical interatomic potential is introduced, which gives a convenient and relatively accurate description of the structural properties and energetics of carbon, including elastic properties, phonons, polytypes, and defects and migration barriers in diamond and graphite.
Abstract: An empirical interatomic potential is introduced, which gives a convenient and relatively accurate description of the structural properties and energetics of carbon, including elastic properties, phonons, polytypes, and defects and migration barriers in diamond and graphite. The potential is applied to study amorphous carbon formed in three different ways. Two resulting structures are similar to experimental $a\ensuremath{-}\mathrm{C}$, but another more diamondlike form has essentially identical energy. The liquid is also found to have unexpected properties.
1,589 citations
IBM1
TL;DR: Strong, anisotropic magnetic relaxation of the field-cooled and zero-field--cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal is reported and interpreted with a thermally activated flux-creep model.
Abstract: We report strong, anisotropic magnetic relaxation of the field-cooled and zero-field-cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal and interpret it with a thermally activated flux-creep model. A simple scaling argument shows that high thermal activation causes magnetic irreversibilities and critical currents to drop below the threshold of detectability at a reduced temperature difference $1\ensuremath{-}t$ proportional to ${H}^{\frac{2}{3}}$, a power frequently observed in experiment and in particular in our crystal.
1,358 citations
TL;DR: It is argued that, if the laws of physics permit an advanced civilization to create and maintain a wormhole in space for interstellar travel, then that wormhole can be converted into a time machine with which causality might be violatable.
Abstract: It is argued that, if the laws of physics permit an advanced civilization to create and maintain a wormhole in space for interstellar travel, then that wormhole can be converted into a time machine with which causality might be violatable. Whether wormholes can be created and maintained entails deep, ill-understood issues about cosmic censorship, quantum gravity, and quantum field theory, including the question of whether field theory enforces an averaged version of the weak energy condition.
1,332 citations
IBM1
TL;DR: The results imply that achieving a high degree of texture both normal to and within the basal plane is important for obtaining very high critical currents in pure polycrystalline samples.
Abstract: The critical current densities across grain boundaries have been measured as a function of misorientation angle in the basal plane of bicrystals of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ For small misorientation angles, the ratio of the grain-boundary critical current density to the bulk critical current density is roughly proportional to the inverse of the misorientation angle; for large angles, this ratio saturates to a value of about $\frac{1}{50}$ These results imply that achieving a high degree of texture both normal to and within the basal plane is important for the obtaining of very high critical currents in pure polycrystalline samples
1,284 citations
TL;DR: A new class of uncertainty relations is derived for pairs of observables in a finite-dimensional Hilbert space which do not have any common eigenvector which contains an ``entropic'' uncertainty relation which improves a previous result of Deutsch and confirms a recent conjecture by Kraus.
Abstract: A new class of uncertainty relations is derived for pairs of observables in a finite-dimensional Hilbert space which do not have any common eigenvector. This class contains an ``entropic'' uncertainty relation which improves a previous result of Deutsch and confirms a recent conjecture by Kraus. Some comments are made on the extension of these relations to the case where the Hilbert space is infinite dimensional.
TL;DR: A phenomenological model, which exploits the diffusive nature of the transport of light, is shown to be in excellent agreement with experimental data for several different scattering geometries, and the dependence on geometry provides an important experimental control over the time scale probed.
Abstract: We obtain useful information from the intensity autocorrelations of light scattered from systems which exhibit strong multiple scattering. A phenomenological model, which exploits the diffusive nature of the transport of light, is shown to be in excellent agreement with experimental data for several different scattering geometries. The dependence on geometry provides an important experimental control over the time scale probed. We call this technique diffusing wave spectroscopy, and illustrate its utility by studying diffusion in a strongly interacting colloidal glass.
TL;DR: L'apparition d'un nouveau mode localise dans un reseau anharmonique pur est predite, mais possede une energie d'activation plus faible.
Abstract: A new kind of localized mode is proposed to occur in a pure anharmonic lattice. Its localization properties are similar to those of a localized mode for a force-constant defect in a harmonic lattice. These modes, which are thermally generated like vacancies but with much smaller activation energies, may appear at cryogenic temperatures in strongly anharmonic solids such as quantum crystals as well as in conventional solids.
TL;DR: A self-consistent mean-field theory predicts a transition from a stationary phase to a chaotic phase occurring at a critical value of the gain parameter.
Abstract: A continuous-time dynamic model of a network of $N$ nonlinear elements interacting via random asymmetric couplings is studied. A self-consistent mean-field theory, exact in the $N\ensuremath{\rightarrow}\ensuremath{\infty}$ limit, predicts a transition from a stationary phase to a chaotic phase occurring at a critical value of the gain parameter. The autocorrelations of the chaotic flow as well as the maximal Lyapunov exponent are calculated.
TL;DR: In this paper, a three-dimensional semiconductor quantum well (quantum dot) has been investigated and the fine structure observed in resonant tunneling through the quantum dot corresponds to the discrete density of states of a zero-dimensional system.
Abstract: Electronic transport through a three-dimensionally confined semiconductor quantum well (``quantum dot'') has been investigated. Fine structure observed in resonant tunneling through the quantum dot corresponds to the discrete density of states of a zero-dimensional system.
TL;DR: The model proposed recently by Yeshurun and Malozemoff to explain the ''irreversibility line'' in high-temperature superconductors is extended to account for the experimentally measured width and shape of the resistive transition in a magnetic field.
Abstract: The model proposed recently by Yeshurun and Malozemoff to explain the "irreversibility line" in high-temperature superconductors is extended to account for the experimentally measured width and shape of the resistive transition in a magnetic field, without invoking material inhomogeneity. It is argues that high ${T}_{c}$ and ${H}_{c2}$ are necessary, but not sufficient, conditions for such materials to show zero resistance at room temperature in substantial magnetic fields.
TL;DR: It is shown that Berry's phase appears in a more general context than realized so far, using some ideas introduced by Pancharatnam in his study of the interference of polarized light to allow a meaningful comparison of the phase between any two nonorthogonal vectors in Hilbert space.
Abstract: It is shown that Berry's phase appears in a more general context than realized so far. The evolution of the quantum system need be neither unitary nor cyclic and may be interrupted by quantum measurements. A key ingredient in this generalization is the use of some ideas introduced by Pancharatnam in his study of the interference of polarized light, which, when carried over to quantum mechanics, allow a meaningful comparison of the phase between any two nonorthogonal vectors in Hilbert space.
TL;DR: A pair of correlated light quanta of 532-nm wavelength with the same linear polarization but divergent directions of propagation was produced by nonlinear optical parametric down conversion and observed a violation of Bell's inequality by 3 standard deviations.
Abstract: A pair of correlated light quanta of 532-nm wavelength with the same linear polarization but divergent directions of propagation was produced by nonlinear optical parametric down conversion. Each light quantum was converted to a definite polarization eigenstate and was reflected by a turning mirror to superpose with the other at a beam splitter. For coincident detection at separated detectors, polarization correlations of the Einstein-Podolsky-Rosen-Bohm type were observed. We also observed a violation of Bell's inequality by 3 standard deviations.
TL;DR: On discute du systeme de liaisons de valence resonnantes a courte distance realise par un gaz de dimeres a cœur dur quantique de densite arbitraire sur un reseau carre a deux dimensions.
Abstract: We discuss the short-range resonating-valence-bond system as realized by a quantum hard-core dimer gas of arbitrary density on a two-dimensional square lattice. When the dimers completely cover the lattice, we argue that there is a first-order transition from a dimer crystal to an insulating quantum liquid state which possesses low-energy, neutral, spinless excitations which we call "resonons." For less than close-packed densities, the ground state is a superfluid. In addition to the usual Goldstone mode, there are low-energy, spinless zone-boundary excitations.
TL;DR: The eAect of on-site Coulomb repulsion on the process of resonant tunneling is studied and it is found that the tunneling peak results from a crossover from the high-temperature Kondo phase to the lowtemperature mixed-valence phase of the system when the chemical potential is varied across the on- site localized-state energy.
Abstract: We study the eAect of on-site Coulomb repulsion on the process of resonant tunneling. We find that the tunneling peak results from a crossover from the high-temperature Kondo phase to the lowtemperature mixed-valence phase of the system when the chemical potential is varied across the on-site localized-state energy. Consequently, the line shape is non-Lorentzian, with rather unusual temperature dependence. Moreover, a magnetic field does not split the tunneling peak, but the line shape is modified. The eAect of coupling between localized states is also discussed, PACS numbers: 71.55.Jv, 73.40.QV In this Letter we discuss the effect of intra-atomic Coulomb interaction on the resonant site in the process of resonant tunneling. Resonant tunneling is thought to be the dominating mechanism for conduction at very low temperature through small systems with localized states. ' In the noninteracting case, this mechanism has been discussed by a number of authors and the phenomenon can be described by a 1D model Hamiltonian Hp, r
TL;DR: Correlation measurements of mixed signal and idler photons produced in the process of parametric down-conversion have been performed as a function of two linear polarizer settings and it is found that the Bell inequality for two separated particles is violated.
Abstract: Correlation measurements of mixed signal and idler photons produced in the process of parametric down-conversion have been performed as a function of two linear polarizer settings. It is found that the Bell inequality for two separated particles is violated by about 6 standard deviations, and that classical probability for light waves is violated substantially also.
TL;DR: In this article, a set of Jastrow wave functions comprises exact eigenstates of a family of S = 1/2$ antiferromagnetic chains with exchange, and the full set of energy levels of this model is obtained; the spectrum exhibits remarkable ''supermultiplet'' degeneracies suggesting the existence of a hidden continuous symmetry.
Abstract: A set of Jastrow wave functions comprises exact eigenstates of a family of S= $\frac{1}{2}$ antiferromagnetic chains with ${\mathrm{r}}^{\mathrm{\ensuremath{-}}2}$ exchange. The ground state of the isotropic model is in this set, and is identical to the U\ensuremath{\rightarrow}\ensuremath{\infty} limit of the Gutzwiller wave function, also identified as Anderson's ``resonating-valence-bond'' state. The full set of energy levels of this model is obtained; the spectrum exhibits remarkable ``supermultiplet'' degeneracies suggesting the existence of a hidden continuous symmetry.
IBM1
TL;DR: It is found that T/sub c/ is constant at approx.36 K from p = 0.15 to 0.24, where it begins to decrease, and beyond papprox. =0.32, superconductivity disappears, even though the samples are more conducting.
Abstract: Samples of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4\ensuremath{-}\ensuremath{\delta}}$ have previously shown a maximum concentration of $p=0.15$ holes per [Cu${\mathrm{O}}_{2}$] unit, because increasing $xg0.15$ normally induces compensating oxygen vacancies. Annealing samples in 100 bars of oxygen pressure fills the oxygen vacancies and greatly increases the range of accessible hole concentrations, up to $p=0.40$ (or effectively ${\mathrm{Cu}}^{+2.40}$). We find that ${T}_{c}$ is constant at \ensuremath{\simeq}36 K from $p=0.15 \mathrm{to} 0.24$, where it begins to decrease. Beyond $p\ensuremath{\simeq}0.32$, superconductivity disappears, even though the samples are more conducting.
TL;DR: The first observation of stochastic resonance in an optical device, the bidirectional ring laser, is reported and the addition of injected noise can lead to an improved signal-to-noise ratio.
Abstract: We report the first observation of stochastic resonance in an optical device, the bidirectional ring laser. The experiment exploits a new technique to modulate periodically the asymmetry between the two counter-rotating lasing modes. The measurements verify that the addition of injected noise can lead to an improved signal-to-noise ratio (relative to that observed with no externally injected noise).
IBM1
TL;DR: It is observed that a strong electric field shifts to higher energies the photoluminescence and photocurrent peaks of a GaAs-${\mathrm{Ga}}_{0.65}$ as superlattice of period D (=65 \AA{}), which is explained by a field-induced localization of carriers to isolated quantum wells.
Abstract: We have observed that a strong electric field $\mathcal{E}$ shifts to higher energies the photoluminescence and photocurrent peaks of a GaAs-${\mathrm{Ga}}_{0.65}$${\mathrm{Al}}_{0.35}$As superlattice of period $D$ (=65 \AA{}), which we explain by a field-induced localization of carriers to isolated quantum wells. Good agreement is found between observed and calculated shifts when the large field-induced increase of the exciton binding energy is taken into account. At moderate fields [\ensuremath{\cong}(2-3)\ifmmode\times\else\texttimes\fi{}${10}^{4}$ V/cm], the coupling between adjacent wells is manifested by four additional peaks that shift at the rates $\ifmmode\pm\else\textpm\fi{}e\mathcal{E}D$ and $\ifmmode\pm\else\textpm\fi{}2e\mathcal{E}D$ and correspond to transitions that involve different levels of the Stark ladder.
TL;DR: In addition to the familiar large local intensity fluctuations, a novel memory eA'ect and long-range correlations in the transmission coefficients which decay to a positive background value are found.
Abstract: The correlation functions of the transmission coefficients for scalar wave propagation through disordered media are calculated by use of both diagrammatic techniques and numerical simulations. The calculation is valid in the diffusive regime: multiple elastic scattering with negligible absorption or inelastic scattering and a scattering length much longer than the wavelength. In addition to the familiar large local intensity fluctuations we find a novel memory effect and long-range correlations in the transmission coefficients which decay to a positive background value. Implications for light-scattering experiments are discussed.
TL;DR: Experimental results generally verify the theoretical predictions of FKLS, but do find one significant difference between experiment and theory — namely, that the exponential decay of C(x) is observed to set in almost immediately with nonzero x, while the theory predicts that its onset should be decelerated.
Abstract: We verify experimentally for optical waves the striking memory effect predicted very recently by Feng, Kane, Lee, and Stone. We present data for both transmission and reflection, and find general agreement with the theoretical predictions for the linear scale dependence and asymptotic exponential falloff of the memory effect. The theoretical and experimental results suggest that significant information about the spatial variation of the incident waveform is preserved during passage through a highly disordered, strongly multiply scattering medium.
TL;DR: The quantization of self-dual two-dimensional Lagrangeans which describe systems that are not explicitly canonical are discussed, and some remarks on the most efficient method for exhibiting the canonical structure are made.
Abstract: Recent Letters and Comments discuss the quantization of self-dual two-dimensional Lagrangeans which describe systems that are not explicitly canonical. We make some remarks on the most efficient method for exhibiting the canonical structure.
TL;DR: In this paper, a new dissipation behavior is reported in superconducting Bi2.2Sr2Ca0.8Cu2Oa+δ for all temperatures below Tc and all magnetic fields exceeding Hc1.
Abstract: A new dissipation behavior is reported in superconducting Bi2.2Sr2Ca0.8Cu2Oa+δfor all temperatures belowTc and all magnetic fields exceeding Hc1. The current-independent electrical resistivity is thermally activated and can be described by an Arrhenius law with a single prefactor and a magnetic-field-and orientation-dependent activation energyU 0 (H,o).This behavior is markedly different from past observations and will be discussed in terms of flux creep and flux flow. This thermally activated behavior implies a finite resistance at all temperatures and all fields exceeding H c1 determined by the activation energy as the only parameter.
TL;DR: A new laser-cooling scheme based on velocity-selective optical pumping of atoms into a nonabsorbing coherent superposition of states is presented, allowing transverse cooling of metastable metastable He atoms to a temperature of 2 K, lower than both the usual Doppler cooling limit and the one-photon recoil energy.
Abstract: We present a new laser-cooling scheme based on velocity-selective optical pumping of atoms into a nonabsorbing coherent superposition of states. This method has allowed us to achieve transverse cooling of metastable $^{4}\mathrm{He}$ atoms to a temperature of 2 \ensuremath{\mu}K, lower than both the usual Doppler cooling limit (23 \ensuremath{\mu}K) and the one-photon recoil energy (4 \ensuremath{\mu}K). The corresponding de Broglie wavelength (1.4 \ensuremath{\mu}m) is larger than the atomic-transition optical wavelength.