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Light-front interpretation of Proton Generalized Polarizabilities ; Lorce, Cédric ; et al in Physical Review Letters (2010), 104 We extend the recently developed formalism to extract light-front quark charge densities from nucleon form factor data to the deformations of these quark charge densities when applying an external ... [more ▼] We extend the recently developed formalism to extract light-front quark charge densities from nucleon form factor data to the deformations of these quark charge densities when applying an external electric field. We show that the resulting induced polarizations can be extracted from proton generalized polarizabilities. The available data for the generalized electric polarizability of the proton yield a pronounced structure in its induced polarization at large transverse distances, which will be pinned down by forthcoming high precision virtual Compton scattering experiments. [less ▲] Detailed reference viewed: 16 (3 ULg)Phases of Polonium via Density Functional Theory Verstraete, Matthieu in Physical Review Letters (2010), 104 Detailed reference viewed: 71 (11 ULg)Rare-earth surface alloying: a new phase for GdAu$_2$ ; Verstraete, Matthieu ; et al in Physical Review Letters (2010), 105 Detailed reference viewed: 119 (11 ULg)Semiclassical Gaps in the Density of States of Chaotic Andreev Billiards ; ; Petitjean, Cyril et al in PHYSICAL REVIEW LETTERS (2010), 104(2), 027001-4 The connection of a superconductor to a chaotic ballistic quantum dot leads to interesting phenomena, most notably the appearance of a hard gap in its excitation spectrum. Here we treat such an Andreev ... [more ▼] The connection of a superconductor to a chaotic ballistic quantum dot leads to interesting phenomena, most notably the appearance of a hard gap in its excitation spectrum. Here we treat such an Andreev billiard semiclassically where the density of states is expressed in terms of the classical trajectories of electrons (and holes) that leave and return to the superconductor. We show how classical orbit correlations lead to the formation of the hard gap, as predicted by random matrix theory in the limit of negligible Ehrenfest time tau(E), and how the influence of a finite tau(E) causes the gap to shrink. Furthermore, for intermediate tau(E) we predict a second gap below E = pi h/2 tau(E) which would presumably be the clearest signature yet of tau(E) effects. [less ▲] Detailed reference viewed: 37 (0 ULg)Polarization vortices in germanium telluride nanoplatelets: A theoretical study Durgun, Engin ; Ghosez, Philippe ; et al in Physical Review Letters (2009), 103 Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict ... [more ▼] Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict the appearance of polarization vortices giving rise to an unusual ferrotoroidic ground state with a spontaneous and reversible toroidal moment of polarization. We highlight the crucial role of inhomogeneous strain in stabilizing polarization vortices. Combined with the phase-change properties of germanium telluride, the ferrotoroidic properties could be of practical interest for ternary logic applications. [less ▲] Detailed reference viewed: 49 (6 ULg)Dynamics of the negative thermal expansion in tellurium based liquid alloys ; Raty, Jean-Yves ; et al in Physical Review Letters (2009), 103(24), 2459014-24590142459014 Negative thermal expansion (NTE) in tellurium based liquid alloys (GeTe 6 and GeTe 12) is analyzed through the atomic vibrational properties. Using neutron inelastic scattering, we show that the ... [more ▼] Negative thermal expansion (NTE) in tellurium based liquid alloys (GeTe 6 and GeTe 12) is analyzed through the atomic vibrational properties. Using neutron inelastic scattering, we show that the structural evolution resulting in the NTE is due to a gain of vibrational entropy that cancels out the Peierls distortion. In the NTE temperature range, these competing effects give rise to noticeable changes in the vibrational density of states spectra. Additional first principles molecular dynamics simulations emphasize the role of the temperature dependance of the Ge atomic environment in this mechanism. For comparison, we extended our study to Ge 2Sb 2Te 5 and Ge 1Sb 2Te 4 phase-change materials. [less ▲] Detailed reference viewed: 58 (3 ULg)Symmetry-Induced Giant Vortex State in a Superconducting Pb Film with a Fivefold Penrose Array of Magnetic Pinning Centers ; Silhanek, Alejandro ; et al in Physical Review Letters (2009), 103(6), A direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained by mapping the local field distribution with a scanning Hall probe microscope. We ... [more ▼] A direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained by mapping the local field distribution with a scanning Hall probe microscope. We demonstrate that stable vortex configurations can be found for fields H similar to 0.8H(1), H(1), and 1.6H(1), where H(1) corresponds to one flux quantum per pinning site. The vortex pattern at 0.8H(1) corresponds to one vacancy in one of the vertices of the thin tiles, whereas at 1.6H(1) the vortex structure can be associated with one interstitial vortex inside each thick tile. Strikingly, for H=1.6H(1), interstitial and pinned vortices arrange themselves in ringlike structures ("vortex corrals") which favor the formation of a giant vortex state at their center. [less ▲] Detailed reference viewed: 14 (0 ULg)How precisely will the total cross section be measured at the LHC? Cudell, Jean-René ; in Physical Review Letters (2009), 102 It is very likely that hadronic scattering will enter a new regime at the LHC, as the black-disk limit is reached. This will lead to a severe change in the t dependence of the real part and of the slope ... [more ▼] It is very likely that hadronic scattering will enter a new regime at the LHC, as the black-disk limit is reached. This will lead to a severe change in the t dependence of the real part and of the slope of the elastic scattering amplitude, and in turn this may bias the measurement of the total cross section. We examine this issue, and suggest new strategies to test the reliability of the total cross section measurements. [less ▲] Detailed reference viewed: 135 (6 ULg)Operational Families of Entanglement Classes for Symmetric N-Qubit States Bastin, Thierry ; Krins, Stéphanie ; Mathonet, Pierre et al in Physical Review Letters (2009), 103 We solve the entanglement classification under stochastic local operations and classical communication (SLOCC) for all multipartite symmetric states in the general N-qubit case. For this purpose, we ... [more ▼] We solve the entanglement classification under stochastic local operations and classical communication (SLOCC) for all multipartite symmetric states in the general N-qubit case. For this purpose, we introduce 2 parameters playing a crucial role, namely, the diversity degree and the degeneracy configuration of a symmetric state. Those parameters give rise to a simple method of identifying operational families of SLOCC entanglement classes of all symmetric N-qubit states, where the number of families grows as the partition function of the number of qubits. [less ▲] Detailed reference viewed: 43 (8 ULg)Operational Determination of Multiqubit Entanglement Classes via Tuning of Local Operations Bastin, Thierry ; ; et al in Physical Review Letters (2009), 102 We present a physical setup with which it is possible to produce arbitrary symmetric long-lived multiqubit entangled states in the internal ground levels of photon emitters, including the paradigmatic ... [more ▼] We present a physical setup with which it is possible to produce arbitrary symmetric long-lived multiqubit entangled states in the internal ground levels of photon emitters, including the paradigmatic Greenberger-Horne-Zeilinger and W states. In the case of three emitters, where each tripartite entangled state belongs to one of two well-defined entanglement classes, we prove a one-to-one correspondence between well-defined sets of experimental parameters, i.e., locally tunable polarizer orientations, and multiqubit entanglement classes inside the symmetric subspace. [less ▲] Detailed reference viewed: 30 (11 ULg)Type-1.5 Superconductivity ; ; et al in Physical Review Letters (2009), 102(11), We demonstrate the existence of a novel superconducting state in high quality two-component MgB(2) single crystalline superconductors where a unique combination of both type-1 (lambda(1)/xi(1)< 1/2) and ... [more ▼] We demonstrate the existence of a novel superconducting state in high quality two-component MgB(2) single crystalline superconductors where a unique combination of both type-1 (lambda(1)/xi(1)< 1/2) and type-2 (lambda(2)/xi(2)> 1/2) superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances, which stabilizes unconventional stripe- and gossamerlike vortex patterns that we have visualized in this type-1.5 superconductor using Bitter decoration and also reproduced in numerical simulations. [less ▲] Detailed reference viewed: 19 (2 ULg)Engineering Multiferroism in CaMnO3 ; Bousquet, Eric ; Ghosez, Philippe in Physical Review Letters (2009), 102 Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic ... [more ▼] Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic perovskite structure of CaMnO3 also exhibits a weak ferroelectric instability. Although ferroelectricity is suppressed by antiferrodistortive motions, we show that it can be favored using strain or chemical engineering in order to make CaMnO3 multiferroic. We finally highlight that the ferroelectric instability of CaMnO3 is Mn-dominated. This illustrates that, contrary to common belief, ferroelectricity and magnetism are not necessarily exclusive but can be driven by the same cation. [less ▲] Detailed reference viewed: 52 (1 ULg)Chaotic bouncing of a droplet on a soap film Gilet, Tristan ; in Physical Review Letters (2009), 102 We examine the complex dynamics arising when a water droplet bounces on a horizontal soap film suspended on a vertically oscillating circular frame. A variety of simple and complex periodic bouncing ... [more ▼] We examine the complex dynamics arising when a water droplet bounces on a horizontal soap film suspended on a vertically oscillating circular frame. A variety of simple and complex periodic bouncing states are observed, in addition to multiperiodicity and period-doubling transitions to chaos. The system is simply and accurately modeled by a single ordinary differential equation, the numerical solution of which captures all the essential features of the observed behavior. Iterative maps and bifurcation diagrams indicate that the system exhibits all the features of a classic low-dimensional chaotic oscillator. [less ▲] Detailed reference viewed: 18 (2 ULg)Coherent backscattering of Bose-Einstein condensates in two-dimensional disorder potentials ; ; et al in Physical Review Letters (2008), 101(2), 020603 We study quantum transport of an interacting Bose-Einstein condensate in a two-dimensional disorder potential. In the limit of a vanishing atom-atom interaction, a sharp cone in the angle-resolved density ... [more ▼] We study quantum transport of an interacting Bose-Einstein condensate in a two-dimensional disorder potential. In the limit of a vanishing atom-atom interaction, a sharp cone in the angle-resolved density of the scattered matter wave is observed, arising from constructive interference between amplitudes propagating along reversed scattering paths. Weak interaction transforms this coherent backscattering peak into a pronounced dip, indicating destructive instead of constructive interference. We reproduce this result, obtained from the numerical integration of the Gross-Pitaevskii equation, by a diagrammatic theory of weak localization in the presence of nonlinearity. [less ▲] Detailed reference viewed: 21 (3 ULg)Time Reversal of Bose-Einstein Condensates Martin, John ; ; in Physical Review Letters (2008), 101 Using Gross-Pitaevskii equation, we study the time reversibility of Bose-Einstein condensates (BEC) in kicked optical lattices, showing that in the regime of quantum chaos, the dynamics can be inverted ... [more ▼] Using Gross-Pitaevskii equation, we study the time reversibility of Bose-Einstein condensates (BEC) in kicked optical lattices, showing that in the regime of quantum chaos, the dynamics can be inverted from explosion to collapse. The accuracy of time reversal decreases with the increase of atom interactions in BEC, until it is completely lost. Surprisingly, quantum chaos helps to restore time reversibility. These predictions can be tested with existing experimental setups. [less ▲] Detailed reference viewed: 36 (9 ULg)Swarming and swirling in self-propelled polar granular rods ; Lumay, Geoffroy ; et al in Physical Review Letters (2008), 100 Using experiments with anisotropic vibrated rods and quasi-2D numerical simulations, we show that shape plays an important role in the collective dynamics of self-propelled (SP) particles. We demonstrate ... [more ▼] Using experiments with anisotropic vibrated rods and quasi-2D numerical simulations, we show that shape plays an important role in the collective dynamics of self-propelled (SP) particles. We demonstrate that SP rods exhibit local ordering, aggregation at the side walls, and clustering absent in round SP particles. Furthermore, we find that at sufficiently strong excitation SP rods engage in a persistent swirling motion in which the velocity is strongly correlated with particle orientation. [less ▲] Detailed reference viewed: 25 (0 ULg)Cooling by Time Reversal of Atomic Matter Waves Martin, John ; ; in Physical Review Letters (2008), 100 We propose an experimental scheme which allows us to realized approximate time reversal of matter waves for ultracold atoms in the regime of quantum chaos. We show that a significant fraction of the atoms ... [more ▼] We propose an experimental scheme which allows us to realized approximate time reversal of matter waves for ultracold atoms in the regime of quantum chaos. We show that a significant fraction of the atoms return back to their original state, being at the same time cooled down by several orders of magnitude. We give a theoretical description of this effect supported by extensive numerical simulations. The proposed scheme can be implemented with existing experimental setups. [less ▲] Detailed reference viewed: 25 (8 ULg)Dynamics of a bouncing droplet onto a vertically vibrated interface Gilet, Tristan ; Terwagne, Denis ; Vandewalle, Nicolas et al in Physical Review Letters (2008), 100(16), Low viscosity (< 100 cSt) silicon oil droplets are placed on a high viscosity (1000 cSt) oil bath that vibrates vertically. The viscosity difference ensures that the droplet is more deformed than the bath ... [more ▼] Low viscosity (< 100 cSt) silicon oil droplets are placed on a high viscosity (1000 cSt) oil bath that vibrates vertically. The viscosity difference ensures that the droplet is more deformed than the bath interface. Droplets bounce periodically on the bath when the acceleration of its sinusoidal motion is larger than a threshold value. The threshold is minimum for a particular frequency of excitation: droplet and bath motions are in resonance. The bouncing droplet has been modeled by considering the deformation of the droplet and the lubrication force exerted by the air layer between the droplet and the bath. Threshold values are predicted and found to be in good agreement with our measurements. [less ▲] Detailed reference viewed: 71 (16 ULg)Charge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism ; Hermann, Raphaël ; et al in Physical Review Letters (2008), 101(22), X- ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). The corresponding charge ... [more ▼] X- ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe= O double layers with antiferroelectric stacking. Diffuse scattering at 360 K, with (1/3 1/3 0) propagation, indicates ferroelectric short- range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled. [less ▲] Detailed reference viewed: 21 (0 ULg)Tetrahedral clustering in molten lithium under pressure ; Raty, Jean-Yves ; in Physical Review Letters (2008), 101(7), 0757034 A series of electronic and structural transitions are predicted in molten lithium from first principles. A new phase with tetrahedral local order characteristic of sp 3 bonded materials and poor ... [more ▼] A series of electronic and structural transitions are predicted in molten lithium from first principles. A new phase with tetrahedral local order characteristic of sp 3 bonded materials and poor electrical conductivity is found at pressures above 150 GPa and temperatures as high as 1000 K. Despite the lack of covalent bonding, weakly bound tetrahedral clusters with finite lifetimes are predicted to exist. The stabilization of this phase in lithium involves a unique mechanism of strong electron localization in interstitial regions and interactions among core electrons. The calculations provide evidence for anomalous melting above 20 GPa, with a melting temperature decreasing below 300 K, and point towards the existence of novel low-symmetry crystalline phases. [less ▲] Detailed reference viewed: 24 (9 ULg) |
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