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  • Erratum: Resonance Effects in Photoemission Time Delays [Phys. Rev. Lett.115, 133001 (2015)]
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    M. Sabbar, S. Heuser, R. Boge, M. Lucchini, T. Carette, E. Lindroth, L. Gallmann, C. Cirelli, and U. Keller

    DOI:https://doi.org/10.1103/PhysRevLett.119.219901

    更新日期:2017-11-20
  • Z3Parafermionic Zero Modes without Andreev Backscattering from the2/3Fractional Quantum Hall State
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Yahya Alavirad, David Clarke, Amit Nag, and Jay D. Sau

    Parafermionic zero modes are a novel set of excitations displaying non-Abelian statistics somewhat richer than that of Majorana modes. These modes are predicted to occur when nearby fractional quantum Hall edge states are gapped by an interposed superconductor. Despite substantial experimental progress, we argue that the necessary crossed Andreev reflection in this arrangement is a challenging milestone to reach. We propose a superconducting quantum dot array structure on a fractional quantum Hall edge that can lead to parafermionic zero modes from coherent superconducting forward scattering on a quantum Hall edge. Such coherent forward scattering has already been demonstrated in recent experiments. We show that for a spin-singlet superconductor interacting with loops of spin unpolarized 2 / 3 fractional quantum edge, even an array size of order 10 should allow one to systematically tune into a parafermionic degeneracy.

    更新日期:2017-11-20
  • Thermodynamic Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov State in theKFe2As2Superconductor
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Chang-woo Cho, Jonathan Haiwei Yang, Noah F. Q. Yuan, Junying Shen, Thomas Wolf, and Rolf Lortz

    We investigate the magnetic phase diagram near the upper critical field of KFe 2 As 2 by magnetic torque and specific heat experiments using a high-resolution piezorotary positioner to precisely control the parallel alignment of the magnetic field with respect to the FeAs layers. We observe a clear double transition when the field is strictly aligned in the plane and a characteristic upturn of the upper critical field line, which goes far beyond the Pauli limit at 4.8 T. This provides firm evidence that a Fulde-Ferrell-Larkin-Ovchinnikov state exists in this iron-based KFe 2 As 2 superconductor.

    更新日期:2017-11-20
  • Observation of Bogoliubov Band Hybridization in the Optimally Doped TrilayerBi2Sr2Ca2Cu3O10+δ
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    So Kunisada, Shintaro Adachi, Shiro Sakai, Nae Sasaki, Mitsuhiro Nakayama, Shuntaro Akebi, Kenta Kuroda, Takao Sasagawa, Takao Watanabe, Shik Shin, and Takeshi Kondo
    更新日期:2017-11-20
  • Correlated Three-Dimensional Imaging of Dislocations: Insights into the Onset of Thermal Slip in Semiconductor Wafers
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    D. Hänschke, A. Danilewsky, L. Helfen, E. Hamann, and T. Baumbach
    更新日期:2017-11-20
  • Instabilities of Jammed Packings of Frictionless Spheres Under Load
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Ning Xu, Andrea J. Liu, and Sidney R. Nagel

    We consider the contribution to the density of vibrational states and the distribution of energy barrier heights of incipient instabilities in a glass modeled by a jammed packing of spheres. On approaching an instability, the frequency of a normal mode and the height of the energy barrier to cross into a new ground state both vanish. These instabilities produce a contribution to the density of vibrational states that scales as ω 3 at low frequencies ω , and a contribution to the distribution of energy barriers Δ H that scales as Δ H − 1 / 3 at low barrier heights.

    更新日期:2017-11-20
  • Correlation between Local Structure Order and Spatial Heterogeneity in a Metallic Glass
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Fan Zhu, Akihiko Hirata, Pan Liu, Shuangxi Song, Yuan Tian, Jiuhui Han, Takeshi Fujita, and Mingwei Chen

    Although nanoscale spatial heterogeneity of metallic glasses has been demonstrated by extensive experimental and theoretical investigations, the nature of spatial heterogeneity remains poorly known owing to the absence of a structural depiction of the inhomogeneity from experimental insight. Here we report the experimental characterization of the spatial heterogeneity of a metallic glass by utilizing state-of-the-art angstrom-beam electron diffraction and scanning transmission electron microscopy. The subnanoscale electron diffraction reveals that the nanoscale spatial heterogeneity and corresponding density fluctuation have a close correlation with the local structure variation from icosahedronlike to tetragonal crystal-like order. The structural insights of spatial heterogeneity have important implications in understanding the properties and dynamics of metallic glasses.

    更新日期:2017-11-20
  • Superfluid Filaments of Dipolar Bosons in Free Space
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Fabio Cinti, Alberto Cappellaro, Luca Salasnich, and Tommaso Macrì

    We systematically investigate the zero temperature phase diagram of bosons interacting via dipolar interactions in three dimensions in free space via path integral Monte Carlo simulations with a few hundreds of particles and periodic boundary conditions based on the worm algorithm. Upon increasing the strength of the dipolar interaction and at sufficiently high densities we find a wide region where filaments are stabilized along the direction of the external field. Most interestingly by computing the superfluid fraction we conclude that the superfluidity is anisotropic and is greatly suppressed along the orthogonal plane. Finally, we perform simulations at finite temperature confirming the stability of the filaments against thermal fluctuations and provide an estimate of the superfluid fraction in the weak coupling limit in the framework of the Landau two-fluid model.

    更新日期:2017-11-20
  • Double Contact During Drop Impact on a Solid Under Reduced Air Pressure
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Er Qiang Li, Kenneth R. Langley, Yuan Si Tian, Peter D. Hicks, and Sigurdur T. Thoroddsen

    Drops impacting on solid surfaces entrap small bubbles under their centers, owing to the lubrication pressure which builds up in the thin intervening air layer. We use ultrahigh-speed interference imaging, at 5 Mfps, to investigate how this air layer changes when the ambient air pressure is reduced below atmospheric. Both the radius and the thickness of the air disc become smaller with reduced air pressure. Furthermore, we find the radial extent of the air disc bifurcates, when the compressibility parameter exceeds ∼ 25 . This bifurcation is also imprinted onto some of the impacts, as a double contact. In addition to the central air disc inside the first ring contact, this is immediately followed by a second ring contact, which entraps an outer toroidal strip of air, which contracts into a ring of bubbles. We find this occurs in a regime where Navier slip, due to rarefied gas effects, enhances the rate gas can escape from the path of the droplet.

    更新日期:2017-11-20
  • What Controls Thermo-osmosis? Molecular Simulations Show the Critical Role of Interfacial Hydrodynamics
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Li Fu, Samy Merabia, and Laurent Joly

    Thermo-osmotic and related thermophoretic phenomena can be found in many situations from biology to colloid science, but the underlying molecular mechanisms remain largely unexplored. Using molecular dynamics simulations, we measure the thermo-osmosis coefficient by both mechanocaloric and thermo-osmotic routes, for different solid-liquid interfacial energies. The simulations reveal, in particular, the crucial role of nanoscale interfacial hydrodynamics. For nonwetting surfaces, thermo-osmotic transport is largely amplified by hydrodynamic slip at the interface. For wetting surfaces, the position of the hydrodynamic shear plane plays a key role in determining the amplitude and sign of the thermo-osmosis coefficient. Finally, we measure a giant thermo-osmotic response of the water-graphene interface, which we relate to the very low interfacial friction displayed by this system. These results open new perspectives for the design of efficient functional interfaces for, e.g., waste-heat harvesting.

    更新日期:2017-11-20
  • Three Dimensional Photonic Dirac Points in Metamaterials
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Qinghua Guo, Biao Yang, Lingbo Xia, Wenlong Gao, Hongchao Liu, Jing Chen, Yuanjiang Xiang, and Shuang Zhang

    Topological semimetals, representing a new topological phase that lacks a full band gap in bulk states and exhibiting nontrivial topological orders, recently have been extended to photonic systems, predominantly in photonic crystals and to a lesser extent metamaterials. Photonic crystal realizations of Dirac degeneracies are protected by various space symmetries, where Bloch modes span the spin and orbital subspaces. Here, we theoretically show that Dirac points can also be realized in effective media through the intrinsic degrees of freedom in electromagnetism under electromagnetic duality. A pair of spin-polarized Fermi-arc-like surface states is observed at the interface between air and the Dirac metamaterials. Furthermore, eigenreflection fields show the decoupling process from a Dirac point to two Weyl points. We also find the topological correlation between a Dirac point and vortex or vector beams in classical photonics. The experimental feasibility of our scheme is demonstrated by designing a realistic metamaterial structure. The theoretical proposal of the photonic Dirac point lays the foundation for unveiling the connection between intrinsic physics and global topology in electromagnetism.

    更新日期:2017-11-20
  • Cavity QED Engineering of Spin Dynamics and Squeezing in a Spinor Gas
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Stuart J. Masson, M. D. Barrett, and Scott Parkins

    We propose a method for engineering spin dynamics in ensembles of integer-spin atoms confined within a high-finesse optical cavity. Our proposal uses cavity-assisted Raman transitions to engineer a Dicke model for integer-spin atoms, which, in a dispersive limit, reduces to effective atom-atom interactions within the ensemble. This scheme offers a promising and flexible new avenue for the exploration of a wide range of spinor many-body physics. As an example of this, we present results showing that this method can be used to generate spin-nematic squeezing in an ensemble of spin-1 atoms. With realistic parameters, the scheme should enable substantial squeezing on time scales much shorter than current experiments with spin-1 Bose-Einstein condensates.

    更新日期:2017-11-20
  • Threshold and Jet Radius Joint Resummation for Single-Inclusive Jet Production
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Xiaohui Liu, Sven-Olaf Moch, and Felix Ringer

    We present the first threshold and jet radius jointly resummed cross section for single-inclusive hadronic jet production. We work at next-to-leading logarithmic accuracy and our framework allows for a systematic extension beyond the currently achieved precision. Long-standing numerical issues are overcome by performing the resummation directly in momentum space within soft collinear effective theory. We present the first numerical results for the LHC and observe an improved description of the available data. Our results are of immediate relevance for LHC precision phenomenology including the extraction of parton distribution functions and the QCD strong coupling constant.

    更新日期:2017-11-20
  • Asymptotic Safety Guaranteed in Supersymmetry
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Andrew D. Bond and Daniel F. Litim

    We explain how asymptotic safety arises in four-dimensional supersymmetric gauge theories. We provide asymptotically safe supersymmetric gauge theories together with their superconformal fixed points, R charges, phase diagrams, and UV-IR connecting trajectories. Strict perturbative control is achieved in a Veneziano limit. Consistency with unitarity and the a theorem is established. We find that supersymmetry enhances the predictivity of asymptotically safe theories.

    更新日期:2017-11-20
  • Probing Sub-GeV Mass Strongly Interacting Dark Matter with a Low-Threshold Surface Experiment
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Jonathan H. Davis

    Using data from the ν -cleus detector, based on the surface of Earth, we place constraints on dark matter in the form of strongly interacting massive particles (SIMPs) which interact with nucleons via nuclear-scale cross sections. For large SIMP-nucleon cross sections, the sensitivity of traditional direct dark matter searches using underground experiments is limited by the energy loss experienced by SIMPs, due to scattering with the rock overburden and experimental shielding on their way to the detector apparatus. Hence, a surface-based experiment is ideal for a SIMP search, despite the much larger background resulting from the lack of shielding. We show using data from a recent surface run of a low-threshold cryogenic detector that values of the SIMP-nucleon cross section up to approximately 10 − 27     cm 2 can be excluded for SIMPs with masses above 100 MeV.

    更新日期:2017-11-20
  • Hořava Gravity is Asymptotically Free in2+1Dimensions
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Andrei O. Barvinsky, Diego Blas, Mario Herrero-Valea, Sergey M. Sibiryakov, and Christian F. Steinwachs

    We compute the β functions of marginal couplings in projectable Hořava gravity in 2 + 1 spacetime dimensions. We show that the renormalization group flow has an asymptotically free fixed point in the ultraviolet (UV), establishing the theory as a UV-complete model with dynamical gravitational degrees of freedom. Therefore, this theory may serve as a toy model to study fundamental aspects of quantum gravity. Our results represent a step forward towards understanding the UV properties of realistic versions of Hořava gravity.

    更新日期:2017-11-20
  • Efficient Low-Order Approximation of First-Passage Time Distributions
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    David Schnoerr, Botond Cseke, Ramon Grima, and Guido Sanguinetti

    We consider the problem of computing first-passage time distributions for reaction processes modeled by master equations. We show that this generally intractable class of problems is equivalent to a sequential Bayesian inference problem for an auxiliary observation process. The solution can be approximated efficiently by solving a closed set of coupled ordinary differential equations (for the low-order moments of the process) whose size scales with the number of species. We apply it to an epidemic model and a trimerization process and show good agreement with stochastic simulations.

    更新日期:2017-11-20
  • Nonlocal Entanglement of 1D Thermal States Induced by Fermion Exchange Statistics
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    YeJe Park, Jeongmin Shim, S.-S. B. Lee, and H.-S. Sim

    When two identical fermions exchange their positions, their wave function gains a phase factor of − 1 . We show that this distance-independent effect can induce nonlocal entanglement in one-dimensional (1D) electron systems having Majorana fermions at the ends. It occurs in the system bulk and has a nontrivial temperature dependence. In a system having a single Majorana fermion at each end, the nonlocal entanglement has a Bell-state form at zero temperature and decays as the temperature increases, vanishing suddenly at a certain finite temperature. In a system having two Majorana fermions at each end, it is in a cluster-state form and its nonlocality is more noticeable at a finite temperature. By contrast, the thermal states of corresponding 1D spins do not have nonlocal entanglement.

    更新日期:2017-11-20
  • Topological Edge States in Periodically Driven Trapped-Ion Chains
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-20
    Pedro Nevado, Samuel Fernández-Lorenzo, and Diego Porras

    Topological insulating phases are primarily associated with condensed-matter systems, which typically feature short-range interactions. Nevertheless, many realizations of quantum matter can exhibit long-range interactions, and it is still largely unknown the effect that these latter may exert upon the topological phases. In this Letter, we investigate the Su-Schrieffer-Heeger topological insulator in the presence of long-range interactions. We show that this model can be readily realized in quantum simulators with trapped ions by means of a periodic driving. Our results indicate that the localization of the associated edge states is enhanced by the long-range interactions, and that the localized components survive within the ground state of the model. These effects could be easily confirmed in current state-of-the-art experimental implementations.

    更新日期:2017-11-20
  • Transition to Turbulent Dynamo Saturation
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Kannabiran Seshasayanan, Basile Gallet, and Alexandros Alexakis

    While the saturated magnetic energy is independent of viscosity in dynamo experiments, it remains viscosity dependent in state-of-the-art 3D direct numerical simulations (DNS). Extrapolating such viscous scaling laws to realistic parameter values leads to an underestimation of the magnetic energy by several orders of magnitude. The origin of this discrepancy is that fully 3D DNS cannot reach low enough values of the magnetic Prandtl number Pm. To bypass this limitation and investigate dynamo saturation at very low Pm, we focus on the vicinity of the dynamo threshold in a rapidly rotating flow: the velocity field then depends on two spatial coordinates only, while the magnetic field consists of a single Fourier mode in the third direction. We perform numerical simulations of the resulting set of reduced equations for Pm down to 2 × 10 − 5 . This parameter regime is currently out of reach to fully 3D DNS. We show that the magnetic energy transitions from a high-Pm viscous scaling regime to a low-Pm turbulent scaling regime, the latter being independent of viscosity. The transition to the turbulent saturation regime occurs at a low value of the magnetic Prandtl number, Pm ≃ 10 − 3 , which explains why it has been overlooked by numerical studies so far.

    更新日期:2017-11-19
  • Forced Imbibition in Porous Media: A Fourfold Scenario
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Céleste Odier, Bertrand Levaché, Enric Santanach-Carreras, and Denis Bartolo

    We establish a comprehensive description of the patterns formed when a wetting liquid displaces a viscous fluid confined in a porous medium. Building on model microfluidic experiments, we evidence four imbibition scenarios all yielding different large-scale morphologies. Combining high-resolution imaging and confocal microscopy, we show that they originate from two liquid-entrainment transitions and a Rayleigh-Plateau instability at the pore scale. Finally, we demonstrate and explain the long-time coarsening of the resulting patterns.

    更新日期:2017-11-17
  • Superconductivity at the Polar-Nonpolar Phase Boundary of SnP with an Unusual Valence State
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    M. Kamitani, M. S. Bahramy, T. Nakajima, C. Terakura, D. Hashizume, T. Arima, and Y. Tokura
    更新日期:2017-11-17
  • Multiple Types of Topological Fermions in Transition Metal Silicides
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Peizhe Tang, Quan Zhou, and Shou-Cheng Zhang

    Exotic massless fermionic excitations with nonzero Berry flux, other than the Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as spin-1 excitations with threefold degeneracy and spin- 3 / 2 Rarita-Schwinger-Weyl fermions. Herein, by using the ab initio density functional theory, we show that these unconventional quasiparticles coexist with type-I and type-II Weyl fermions in a family of transition metal silicides, including CoSi, RhSi, RhGe, and CoGe, when spin-orbit coupling is considered. Their nontrivial topology results in a series of extensive Fermi arcs connecting projections of these bulk excitations on the side surface, which is confirmed by (001) surface electronic spectra of CoSi. In addition, these stable arc states exist within a wide energy window around the Fermi level, which makes them readily accessible in angle-resolved photoemission spectroscopy measurements.

    更新日期:2017-11-17
  • Unconventional Chiral Fermions and Large Topological Fermi Arcs in RhSi
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Guoqing Chang, Su-Yang Xu, Benjamin J. Wieder, Daniel S. Sanchez, Shin-Ming Huang, Ilya Belopolski, Tay-Rong Chang, Songtian Zhang, Arun Bansil, Hsin Lin, and M. Zahid Hasan

    The theoretical proposal of chiral fermions in topological semimetals has led to a significant effort towards their experimental realization. In particular, the Fermi surfaces of chiral semimetals carry quantized Chern numbers, making them an attractive platform for the observation of exotic transport and optical phenomena. While the simplest example of a chiral fermion in condensed matter is a conventional | C | = 1 Weyl fermion, recent theoretical works have proposed a number of unconventional chiral fermions beyond the standard model which are protected by unique combinations of topology and crystalline symmetries. However, materials candidates for experimentally probing the transport and response signatures of these unconventional fermions have thus far remained elusive. In this Letter, we propose the RhSi family in space group No. 198 as the ideal platform for the experimental examination of unconventional chiral fermions. We find that RhSi is a filling-enforced semimetal that features near its Fermi surface a chiral double sixfold-degenerate spin-1 Weyl node at R and a previously uncharacterized fourfold-degenerate chiral fermion at Γ . Each unconventional fermion displays Chern number ± 4 at the Fermi level. We also show that RhSi displays the largest possible momentum separation of compensative chiral fermions, the largest proposed topologically nontrivial energy window, and the longest possible Fermi arcs on its surface. We conclude by proposing signatures of an exotic bulk photogalvanic response in RhSi.

    更新日期:2017-11-17
  • Ultrafast Generation of Unconventional{001}Loops in Si
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Luis A. Marqués, María Aboy, Iván Santos, Pedro López, Fuccio Cristiano, Antonino La Magna, Karim Huet, Toshiyuki Tabata, and Lourdes Pelaz

    Ultrafast laser annealing of ion implanted Si has led to thermodynamically unexpected large { 001 } self-interstitial loops, and the failure of Ostwald ripening models for describing self-interstitial cluster growth. We have carried out molecular dynamics simulations in combination with focused experiments in order to demonstrate that at temperatures close to the melting point, self-interstitial rich Si is driven into dense liquidlike droplets that are highly mobile within the solid crystalline Si matrix. These liquid droplets grow by a coalescence mechanism and eventually transform into { 001 } loops through a liquid-to-solid phase transition in the nanosecond time scale.

    更新日期:2017-11-17
  • Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    M. J. Martin, W. Gekelman, B. Van Compernolle, P. Pribyl, and T. Carter

    An experiment in a linear device, the Large Plasma Device, is used to study sheaths caused by an actively powered radio frequency (rf) antenna. The rf antenna used in the experiment consists of a single current strap recessed inside a copper box enclosure without a Faraday screen. A large increase in the plasma potential was observed along magnetic field lines that connect to the antenna limiter. The electric field from the spatial variation of the rectified plasma potential generated E → × B → 0 flows, often referred to as convective cells. The presence of the flows generated by these potentials is confirmed by Mach probes. The observed convective cell flows are seen to cause the plasma in front of the antenna to flow away and cause a density modification near the antenna edge. These can cause hot spots and damage to the antenna and can result in a decrease in the ion cyclotron range of frequencies antenna coupling.

    更新日期:2017-11-17
  • Unexpected Sensitivity of Nitrogen Ions Superradiant Emission on Pump Laser Wavelength and Duration
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Yi Liu, Pengji Ding, Neven Ibrakovic, Samuel Bengtsson, Shihua Chen, Rostyslav Danylo, Emma R. Simpson, Esben W. Larsen, Xiang Zhang, Zhengquan Fan, Aurélien Houard, Johan Mauritsson, Anne L’Huillier, Cord L. Arnold, Songlin Zhuang, Vladimir Tikhonchuk, and André Mysyrowicz

    Nitrogen molecules in ambient air exposed to an intense near-infrared femtosecond laser pulse give rise to cavity-free superradiant emission at 391.4 and 427.8 nm. An unexpected pulse duration-dependent cyclic variation of the superradiance intensity is observed when the central wavelength of the femtosecond pump laser pulse is finely tuned between 780 and 820 nm, and no signal occurs at the resonant wavelength of 782.8 nm ( 2 ω 782.8     nm = ω 391.4     nm ). On the basis of a semiclassical recollision model, we show that an interference of dipolar moments of excited ions created by electron recollisions explains this behavior.

    更新日期:2017-11-17
  • Topological Edge-State Manifestation of Interacting 2D Condensed Boson-Lattice Systems in a Harmonic Trap
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Bogdan Galilo, Derek K. K. Lee, and Ryan Barnett

    In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states. We also find that the number of edge states crossing the gap is increased in the presence of a harmonic trap, and the edge modes experience an energy shift while traversing the first Brillouin zone which is related to the topological properties of the system. We find an analytical expression for the edge-state energies and our comparison with numerical computation shows excellent agreement.

    更新日期:2017-11-17
  • Long-Lived Inverse Chirp Signals from Core-Collapse in Massive Scalar-Tensor Gravity
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-17
    Ulrich Sperhake, Christopher J. Moore, Roxana Rosca, Michalis Agathos, Davide Gerosa, and Christian D. Ott

    This Letter considers stellar core collapse in massive scalar-tensor theories of gravity. The presence of a mass term for the scalar field allows for dramatic increases in the radiated gravitational wave signal. There are several potential smoking gun signatures of a departure from general relativity associated with this process. These signatures could show up within existing LIGO-Virgo searches.

    更新日期:2017-11-17
  • 更新日期:2017-11-17
  • Block Analysis for the Calculation of Dynamic and Static Length Scales in Glass-Forming Liquids
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Saurish Chakrabarty, Indrajit Tah, Smarajit Karmakar, and Chandan Dasgupta

    We present block analysis, an efficient method of performing finite-size scaling for obtaining the length scale of dynamic heterogeneity and the point-to-set length scale for generic glass-forming liquids. This method involves considering blocks of varying sizes embedded in a system of a fixed (large) size. The length scale associated with dynamic heterogeneity is obtained from a finite-size scaling analysis of the dependence of the four-point dynamic susceptibility on the block size. The block size dependence of the variance of the α relaxation time yields the static point-to-set length scale. The values of the obtained length scales agree quantitatively with those obtained from other conventional methods. This method provides an efficient experimental tool for studying the growth of length scales in systems such as colloidal glasses for which performing finite-size scaling by carrying out experiments for varying system sizes may not be feasible.

    更新日期:2017-11-17
  • Magnetospheric Multiscale Observation of Plasma Velocity-Space Cascade: Hermite Representation and Theory
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    S. Servidio, A. Chasapis, W. H. Matthaeus, D. Perrone, F. Valentini, T. N. Parashar, P. Veltri, D. Gershman, C. T. Russell, B. Giles, S. A. Fuselier, T. D. Phan, and J. Burch

    Plasma turbulence is investigated using unprecedented high-resolution ion velocity distribution measurements by the Magnetospheric Multiscale mission (MMS) in the Earth’s magnetosheath. This novel observation of a highly structured particle distribution suggests a cascadelike process in velocity space. Complex velocity space structure is investigated using a three-dimensional Hermite transform, revealing, for the first time in observational data, a power-law distribution of moments. In analogy to hydrodynamics, a Kolmogorov approach leads directly to a range of predictions for this phase-space transport. The scaling theory is found to be in agreement with observations. The combined use of state-of-the-art MMS data sets, novel implementation of a Hermite transform method, and scaling theory of the velocity cascade opens new pathways to the understanding of plasma turbulence and the crucial velocity space features that lead to dissipation in plasmas.

    更新日期:2017-11-17
  • Revision of Bubble Bursting: Universal Scaling Laws of Top Jet Drop Size and Speed
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Alfonso M. Gañán-Calvo

    The collapse of a bubble of radius R o at the surface of a liquid generating a liquid jet and a subsequent first drop of radius R is universally scaled using the Ohnesorge number Oh = μ / ( ρ σ R o ) 1 / 2 and a critical value Oh * below which no droplet is ejected; ρ , σ , and μ are the liquid density, surface tension, and viscosity, respectively. First, a flow field analysis at ejection yields the scaling of R with the jet velocity V as R / l μ ∼ ( V / V μ ) − 5 / 3 , where l μ = μ 2 / ( ρ σ ) and V μ = σ / μ . This resolves the scaling problem of curvature reversal, a prelude to jet formation. In addition, the energy necessary for the ejection of a jet with a volume and averaged velocity proportional to R o R 2 and V , respectively, comes from the energy excess from the total available surface energy, proportional to σ R o 2 , minus the one dissipated by viscosity, proportional to μ ( σ R o 3 / ρ ) 1 / 2 . Using the scaling variable φ = ( Oh * − Oh ) Oh − 2 , it yields V / V μ = k v φ − 3 / 4 and R / l μ = k d φ 5 / 4 , which collapse published data since 1954 and resolve the scaling of R and V with k v = 16 , k d = 0.6 , and Oh * = 0.043 when gravity effects are negligible.

    更新日期:2017-11-17
  • Persistence and Lifelong Fidelity of Phase Singularities in Optical Random Waves
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    L. De Angelis, F. Alpeggiani, A. Di Falco, and L. Kuipers

    Phase singularities are locations where light is twisted like a corkscrew, with positive or negative topological charge depending on the twisting direction. Among the multitude of singularities arising in random wave fields, some can be found at the same location, but only when they exhibit opposite topological charge, which results in their mutual annihilation. New pairs can be created as well. With near-field experiments supported by theory and numerical simulations, we study the persistence and pairing statistics of phase singularities in random optical fields as a function of the excitation wavelength. We demonstrate how such entities can encrypt fundamental properties of the random fields in which they arise.

    更新日期:2017-11-17
  • Propagation Dynamics Associated with Resonant Magnetic Perturbation Fields in High-Confinement Mode Plasmas inside the KSTAR Tokamak
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    W. W. Xiao, T. E. Evans, G. R. Tynan, S. W. Yoon, Y. M. Jeon, W. H. Ko, Y. U. Nam, Y. K. Oh, and KSTAR team

    The propagation dynamics of resonant magnetic perturbation fields in KSTAR H -mode plasmas with injection of small edge perturbations produced by a supersonic molecular beam injection is reported for the first time. The results show that the perturbation field first excites a plasma response on the q = 3 magnetic surface and then propagates inward to the q = 2 surface with a radially averaged propagation velocity of resonant magnetic perturbations field equal to 32.5     m /   s . As a result, the perturbation field brakes the toroidal rotation on the q = 3 surface first causing a momentum transport perturbation that propagates both inward and outward. A higher density fluctuation level is observed. The propagation velocity of the resonant magnetic perturbations field is larger than the radial propagation velocity of the perturbation in the toroidal rotation.

    更新日期:2017-11-16
  • Optimal Design of Experiments by Combining Coarse and Fine Measurements
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Alpha A. Lee, Michael P. Brenner, and Lucy J. Colwell

    In many contexts, it is extremely costly to perform enough high-quality experimental measurements to accurately parametrize a predictive quantitative model. However, it is often much easier to carry out large numbers of experiments that indicate whether each sample is above or below a given threshold. Can many such categorical or “coarse” measurements be combined with a much smaller number of high-resolution or “fine” measurements to yield accurate models? Here, we demonstrate an intuitive strategy, inspired by statistical physics, wherein the coarse measurements are used to identify the salient features of the data, while the fine measurements determine the relative importance of these features. A linear model is inferred from the fine measurements, augmented by a quadratic term that captures the correlation structure of the coarse data. We illustrate our strategy by considering the problems of predicting the antimalarial potency and aqueous solubility of small organic molecules from their 2D molecular structure.

    更新日期:2017-11-16
  • Wall Slip of Soft-Jammed Systems: A Generic Simple Shear Process
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    X. Zhang, E. Lorenceau, P. Basset, T. Bourouina, F. Rouyer, J. Goyon, and P. Coussot

    From well-controlled long creep tests, we show that the residual apparent yield stress observed with soft-jammed systems along smooth surfaces is an artifact due to edge effects. By removing these effects, we can determine the stress solely associated with steady-state wall slip below the material yield stress. This stress is found to vary linearly with the slip velocity for a wide range of materials whatever the structure, the interaction types between the elements and with the wall, and the concentration. Thus, wall slip results from the laminar flow of some given free liquid volume remaining between the (rough) jammed structure formed by the elements and the smooth wall. This phenomenon may be described by the simple shear flow in a Newtonian liquid layer of uniform thickness. For various systems, this equivalent thickness varies in a narrow range ( 35 ± 15     nm ).

    更新日期:2017-11-16
  • Band Structure and Contact Resistance of Carbon Nanotubes Deformed by a Metal Contact
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Roohollah Hafizi, Jerry Tersoff, and Vasili Perebeinos

    Capillary and van der Waals forces cause nanotubes to deform or even collapse under metal contacts. Using ab initio band structure calculations, we find that these deformations reduce the band gap by as much as 30%, while fully collapsed nanotubes become metallic. Moreover, degeneracy lifting due to the broken axial symmetry, and wave functions mismatch between the fully collapsed and the round portions of a CNT, lead to a 3 times higher contact resistance. The latter we demonstrate by contact resistance calculations within the tight-binding approach.

    更新日期:2017-11-16
  • Favorable Concurrence of Static and Dynamic Phenomena at the Morphotropic Phase Boundary ofxBiNi0.5Zr0.5O3−(1−x)PbTiO3
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    K. Datta, R. B. Neder, J. Chen, J. C. Neuefeind, and B. Mihailova

    We reveal that concurrent events of inherent entropy boosting and increased synchronization between A - and B -site cation vibrations of an A B O 3 -type perovskite structure give rise to a larger piezoelectric response in a ferroelectric system at its morphotropic phase boundary (MPB). It is further evident that the superior piezoelectric properties of x BiNi 0.5 Zr 0.5 O 3 − ( 1 − x ) PbTiO 3 in comparison to x BiNi 0.5 Ti 0.5 O 3 − ( 1 − x ) PbTiO 3 are due to the absolute flattening of the local potentials for all ferroelectrically active cations with a higher spontaneous polarization at the MPB. These distinctive features are discovered from the analyses of neutron pair distribution functions and Raman scattering data at ambient conditions, which are particularly sensitive to mesoscopic-scale structural correlations. Altogether this uncovers more fundamental structure-property connections for ferroelectric systems exhibiting a MPB, and thereby has a critical impact in contriving efficient novel materials.

    更新日期:2017-11-16
  • Angular Momentum of Topologically Structured Darkness
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Samuel N. Alperin and Mark E. Siemens

    We theoretically analyze and experimentally measure the extrinsic angular momentum contribution of topologically structured darkness found within fractional vortex beams, and show that this structured darkness can be explained by evanescent waves at phase discontinuities in the generating optic. We also demonstrate the first direct measurement of the intrinsic orbital angular momentum of light with both intrinsic and extrinsic angular momentum, and explain why the total orbital angular momenta of fractional vortices do not match the winding number of their generating phases.

    更新日期:2017-11-16
  • Probing Positron Cooling in Noble Gases via AnnihilationγSpectra
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    D. G. Green

    γ spectra for positron annihilation in noble-gas atoms are calculated using many-body theory for positron momenta up to the positronium-formation threshold. These data are used, together with time-evolving positron-momentum distributions determined in the preceding Letter [Phys. Rev. Lett. 119, 203403 (2017)], to calculate the time-varying γ spectra produced during positron cooling in noble gases. The γ spectra and their S ¯ and W ¯ shape parameters are shown to be sensitive probes of the time evolution of the positron momentum distribution and thus provide a means of studying positron cooling that is complementary to positron lifetime spectroscopy.

    更新日期:2017-11-16
  • Positron Cooling and Annihilation in Noble Gases
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    D. G. Green

    Positron cooling and annihilation in room temperature noble gases is simulated using accurate scattering and annihilation cross sections calculated with many-body theory, enabling the first simultaneous probing of the energy dependence of the scattering and annihilation cross sections. A strikingly small fraction of positrons is shown to survive to thermalization: ∼ 0.1 in He, ∼ 0 in Ne, ∼ 0.15 in Ar, ∼ 0.05 in Kr, and ∼ 0.01 in Xe. For Xe, the time-varying annihilation rate Z ¯ eff ( τ ) is shown to be highly sensitive to the depletion of the momentum distribution due to annihilation, conclusively explaining the long-standing discrepancy between gas-cell and trap-based measurements. Overall, the use of the accurate atomic data gives Z ¯ eff ( τ ) in close agreement with experiment for all noble gases except Ne, the experiment for which is proffered to have suffered from incomplete knowledge of the fraction of positrons surviving to thermalization and/or the presence of impurities.

    更新日期:2017-11-16
  • Geiger-Nuttall Law for Nuclei in Strong Electromagnetic Fields
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    D. S. Delion and S. A. Ghinescu

    We investigate the influence of a strong laser electromagnetic field on the α -decay rate by using the Hennenberger frame of reference. We introduce an adimensional parameter D = S 0 / R 0 , where R 0 is the geometrical nuclear radius and S 0 ∼ I / ω 2 is a length parameter depending on the laser intensity I and frequency ω . We show that the barrier penetrability has a strong increase for intensities corresponding to D > D crit = 1 , due to the fact that the resulting Coulomb potential becomes strongly anisotropic even for spherical nuclei. As a consequence, the contribution of the monopole term increases the barrier penetrability by 2 orders of magnitude, while the total contribution has an effect of 6 orders of magnitude at D ∼ 3 D crit . In the case of deformed nuclei, the electromagnetic field increases the penetrability by an additional order of magnitude for a quadrupole deformation β 2 ∼ 0.3 . The influence of the electromagnetic field can be expressed in terms of a shifted Geiger-Nuttal law by a term depending on S 0 and deformation.

    更新日期:2017-11-16
  • Double-Cascade Events from New Physics in Icecube
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Pilar Coloma, Pedro A. N. Machado, Ivan Martinez-Soler, and Ian M. Shoemaker

    A variety of new physics models allows for neutrinos to up-scatter into heavier states. If the incident neutrino is energetic enough, the heavy neutrino may travel some distance before decaying. In this work, we consider the atmospheric neutrino flux as a source of such events. At IceCube, this would lead to a “double-bang” (DB) event topology, similar to what is predicted to occur for tau neutrinos at ultrahigh energies. The DB event topology has an extremely low background rate from coincident atmospheric cascades, making this a distinctive signature of new physics. Our results indicate that IceCube should already be able to derive new competitive constraints on models with GeV-scale sterile neutrinos using existing data.

    更新日期:2017-11-16
  • Lorentz Symmetry Violations from Matter-Gravity Couplings with Lunar Laser Ranging
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    A. Bourgoin, C. Le Poncin-Lafitte, A. Hees, S. Bouquillon, G. Francou, and M.-C. Angonin
    更新日期:2017-11-16
  • Superconducting-Gravimeter Tests of Local Lorentz Invariance
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Natasha A. Flowers, Casey Goodge, and Jay D. Tasson
    更新日期:2017-11-16
  • Digital Quantum Estimation
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Majid Hassani, Chiara Macchiavello, and Lorenzo Maccone

    Quantum metrology calculates the ultimate precision of all estimation strategies, measuring what is their root-mean-square error (RMSE) and their Fisher information. Here, instead, we ask how many bits of the parameter we can recover; namely, we derive an information-theoretic quantum metrology. In this setting, we redefine “Heisenberg bound” and “standard quantum limit” (the usual benchmarks in the quantum estimation theory) and show that the former can be attained only by sequential strategies or parallel strategies that employ entanglement among probes, whereas parallel-separable strategies are limited by the latter. We highlight the differences between this setting and the RMSE-based one.

    更新日期:2017-11-16
  • Interaction Dependent Heating and Atom Loss in a Periodically Driven Optical Lattice
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-16
    Martin Reitter, Jakob Näger, Karen Wintersperger, Christoph Sträter, Immanuel Bloch, André Eckardt, and Ulrich Schneider
    更新日期:2017-11-16
  • Lattice Model to Derive the Fluctuating Hydrodynamics of Active Particles with Inertia
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    A. Manacorda and A. Puglisi

    We derive the hydrodynamic equations with fluctuating currents for the density, momentum, and energy fields for an active system in the dilute limit. In our model, nonoverdamped self-propelled particles (such as grains or birds) move on a lattice, interacting by means of aligning dissipative forces and excluded volume repulsion. Our macroscopic equations, in a specific case, reproduce a transition line from a disordered phase to a swarming phase and a linear dispersion law accounting for underdamped wave propagation. Numerical simulations up to a packing fraction ∼10% are in fair agreement with the theory, including the macroscopic noise amplitudes. At a higher packing fraction, a dense-diluted coexistence emerges. We underline the analogies with the granular kinetic theories, elucidating the relation between the active swarming phase and granular shear instability.

    更新日期:2017-11-16
  • Flow of Deformable Droplets: Discontinuous Shear Thinning and Velocity Oscillations
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    M. Foglino, A. N. Morozov, O. Henrich, and D. Marenduzzo

    We study the rheology of a suspension of soft deformable droplets subjected to a pressure-driven flow. Through computer simulations, we measure the apparent viscosity as a function of droplet concentration and pressure gradient, and provide evidence of a discontinuous shear thinning behavior, which occurs at a concentration-dependent value of the forcing. We further show that this response is associated with a nonequilibrium transition between a “hard” (or less deformable) phase, which is nearly jammed and flows very slowly, and a “soft” (or more deformable) phase, which flows much more easily. The soft phase is characterized by flow-induced time dependent shape deformations and internal currents, which are virtually absent in the hard phase. Close to the transition, we find sustained oscillations in both the droplet and fluid velocities. Polydisperse systems show similar phenomenology but with a smoother transition, and less regular oscillations.

    更新日期:2017-11-16
  • Optimizing Hyperuniformity in Self-Assembled Bidisperse Emulsions
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Joshua Ricouvier, Romain Pierrat, Rémi Carminati, Patrick Tabeling, and Pavel Yazhgur

    We study long range density fluctuations (hyperuniformity) in two-dimensional jammed packings of bidisperse droplets. Taking advantage of microfluidics, we systematically span a large range of size and concentration ratios of the two droplet populations. We identify various defects increasing long range density fluctuations mainly due to organization of local particle environment. By choosing an appropriate bidispersity, we fabricate materials with a high level of hyperuniformity. Interesting transparency properties of these optimized materials are established based on numerical simulations.

    更新日期:2017-11-16
  • Competition between Chaotic and Nonchaotic Phases in a Quadratically Coupled Sachdev-Ye-Kitaev Model
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Xin Chen, Ruihua Fan, Yiming Chen, Hui Zhai, and Pengfei Zhang

    The Sachdev-Ye-Kitaev (SYK) model is a concrete solvable model to study non-Fermi liquid properties, holographic duality, and maximally chaotic behavior. In this work, we consider a generalization of the SYK model that contains two SYK models with a different number of Majorana modes coupled by quadratic terms. This model is also solvable, and the solution shows a zero-temperature quantum phase transition between two non-Fermi liquid chaotic phases. This phase transition is driven by tuning the ratio of two mode numbers, and a nonchaotic Fermi liquid sits at the critical point with an equal number of modes. At a finite temperature, the Fermi liquid phase expands to a finite regime. More intriguingly, a different non-Fermi liquid phase emerges at a finite temperature. We characterize the phase diagram in terms of the spectral function, the Lyapunov exponent, and the entropy. Our results illustrate a concrete example of the quantum phase transition and critical behavior between two non-Fermi liquid phases.

    更新日期:2017-11-16
  • Solvable Sachdev-Ye-Kitaev Models in Higher Dimensions: From Diffusion to Many-Body Localization
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Shao-Kai Jian and Hong Yao

    Many aspects of many-body localization (MBL) transitions remain elusive so far. Here, we propose a higher-dimensional generalization of the Sachdev-Ye-Kitaev (SYK) model and show that it exhibits a MBL transition. The model on a bipartite lattice has N Majorana fermions with SYK interactions on each site of the A sublattice and M free Majorana fermions on each site of the B sublattice, where N and M are large and finite. For r≡M/N<rc=1, it describes a diffusive metal exhibiting maximal chaos. Remarkably, its diffusive constant D vanishes [D∝(rc−r)1/2] as r→rc, implying a dynamical transition to a MBL phase. It is further supported by numerical calculations of level statistics which changes from Wigner-Dyson (r<rc) to Poisson (r>rc) distributions. Note that no subdiffusive phase intervenes between diffusive and MBL phases. Moreover, the critical exponent ν=0, violating the Harris criterion. Our higher-dimensional SYK model may provide a promising arena to explore exotic MBL transitions.

    更新日期:2017-11-16
  • Generating Carrier-Envelope-Phase Stabilized Few-Cycle Pulses from a Free-Electron Laser Oscillator
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Ryoichi Hajima and Ryoji Nagai

    We propose a scheme to generate carrier-envelope-phase (CEP) stabilized few-cycle optical pulses from a free-electron laser oscillator. The CEP stabilization is realized by the continuous injection of CEP-stabilized seed pulses from an external laser to the free-electron laser oscillator whose cavity length is perfectly synchronized to the electron bunch repetition. Operated at a midinfrared wavelength, the proposed method is able to drive a photon source based on high harmonic generation (HHG) to explore the generation of isolated attosecond pulses at photon energies above 1 keV with a repetition of >10  MHz. The HHG photon source will open a door to full-scale experiments of attosecond x-ray pulses and push ultrafast laser science to the zeptosecond regime.

    更新日期:2017-11-16
  • Different Time Scales in the Dissociation Dynamics of Core-ExcitedCF4by Two Internal Clocks
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    H. Iwayama, C. Léonard, F. Le Quéré, S. Carniato, R. Guillemin, M. Simon, M. N. Piancastelli, and E. Shigemasa

    Fragmentation processes following C 1s→lowest unoccupied molecular orbital core excitations in CF4 have been analyzed on the ground of the angular distribution of the CF3+ emitted fragments by means of Auger electron-photoion coincidences. Different time scales have been enlightened, which correspond to either ultrafast fragmentation, on the few-femtosecond scale, where the molecule has no time to rotate and the fragments are emitted according to the maintained orientation of the core-excited species, or dissociation after resonant Auger decay, where the molecule still keeps some memory of the excitation process before reassuming random orientation. Potential energy surfaces of the ground, core-excited, and final states have been calculated at the ab initio level, which show the dissociative nature of the neutral excited state, leading to ultrafast dissociation, as well as the also dissociative nature of some of the final ionic states reached after resonant Auger decay, yielding the same fragments on a much longer time scale.

    更新日期:2017-11-16
  • Comparison Study of Strong-Field Ionization of Molecules and Atoms by Bicircular Two-Color Femtosecond Laser Pulses
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Kang Lin, Xinyan Jia, Zuqing Yu, Feng He, Junyang Ma, Hui Li, Xiaochun Gong, Qiying Song, Qinying Ji, Wenbin Zhang, Hanxiao Li, Peifen Lu, Heping Zeng, Jing Chen, and Jian Wu

    We experimentally investigate the single and double ionization of N2 and O2 molecules in bicircular two-color femtosecond laser pulses, and compare with their companion atoms of Ar and Xe with comparable ionization thresholds. Electron recollision assisted enhanced ionization is observed in N2 and Ar by controlling the helicity and field ratio between the two colors, whereas the enhanced ionization via the recollision is almost absent in O2 and Xe. Our S-matrix simulations clearly reveal the crucial role of the detailed electronic structures of N2 and O2 on the two-dimensional recollision of the electrons driven by the bicircular two-color laser fields. As compared to Ar, the resonant multiphoton excitation dominates the double ionization of Xe.

    更新日期:2017-11-16
  • Signatures of Electronic Structure in Bicircular High-Harmonic Spectroscopy
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Denitsa Baykusheva, Simon Brennecke, Manfred Lein, and Hans Jakob Wörner

    High-harmonic spectroscopy driven by circularly polarized laser pulses and their counterrotating second harmonic is a new branch of attosecond science which currently lacks quantitative interpretations. We extend this technique to the midinfrared regime and record detailed high-harmonic spectra of several rare-gas atoms. These results are compared with the solution of the Schrödinger equation in three dimensions and calculations based on the strong-field approximation that incorporate accurate scattering-wave recombination matrix elements. A quantum-orbit analysis of these results provides a transparent interpretation of the measured intensity ratios of symmetry-allowed neighboring harmonics in terms of (i) a set of propensity rules related to the angular momentum of the atomic orbitals, (ii) atom-specific matrix elements related to their electronic structure, and (iii) the interference of the emissions associated with electrons in orbitals corotating or counterrotating with the laser fields. These results provide the foundation for a quantitative understanding of bicircular high-harmonic spectroscopy.

    更新日期:2017-11-16
  • First Exclusive Measurement of Deeply Virtual Compton Scattering offHe4: Toward the 3D Tomography of Nuclei
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    M. Hattawyet al.(CLAS Collaboration)

    We report on the first measurement of the beam-spin asymmetry in the exclusive process of coherent deeply virtual Compton scattering off a nucleus. The experiment uses the 6 GeV electron beam from the Continuous Electron Beam Accelerator Facility (CEBAF) accelerator at Jefferson Lab incident on a pressurized He4 gaseous target placed in front of the CEBAF Large Acceptance Spectrometer (CLAS). The scattered electron is detected by CLAS and the photon by a dedicated electromagnetic calorimeter at forward angles. To ensure the exclusivity of the process, a specially designed radial time projection chamber is used to detect the recoiling He4 nuclei. We measure beam-spin asymmetries larger than those observed on the free proton in the same kinematic domain. From these, we are able to extract, in a model-independent way, the real and imaginary parts of the only He4 Compton form factor, HA. This first measurement of coherent deeply virtual Compton scattering on the He4 nucleus, with a fully exclusive final state via nuclear recoil tagging, leads the way toward 3D imaging of the partonic structure of nuclei.

    更新日期:2017-11-16
  • Heavy-Quark Symmetry Implies Stable Heavy Tetraquark MesonsQiQjq¯kq¯l
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Estia J. Eichten and Chris Quigg
    更新日期:2017-11-16
  • Discovery of the Doubly CharmedΞccBaryon Implies a Stablebbu¯d¯Tetraquark
    Phys. Rev. Lett. (IF 8.462) Pub Date : 2017-11-15
    Marek Karliner and Jonathan L. Rosner
    更新日期:2017-11-16
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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