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See detailHotspot Decorations Map Plasmonic Patterns with the Resolution of Scanning Probe Techniques
Valev, V. K.; Silhanek, Alejandro ULg; Jeyaram, Y. et al

in Physical Review Letters (2011), 106(22),

In high definition mapping of the plasmonic patterns on the surfaces of nanostructures, the diffraction limit of light remains an important obstacle. Here we demonstrate that this diffraction limit can be ... [more ▼]

In high definition mapping of the plasmonic patterns on the surfaces of nanostructures, the diffraction limit of light remains an important obstacle. Here we demonstrate that this diffraction limit can be completely circumvented. We show that upon illuminating nanostructures made of nickel and palladium, the resulting surface-plasmon pattern is imprinted on the structures themselves; the hotspots (regions of local field enhancement) are decorated with overgrowths, allowing for their subsequent imaging with scanning-probe techniques. The resulting resolution of plasmon pattern imaging is correspondingly improved. [less ▲]

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See detailUnexpectedly Large Electronic Contribution to Linear Magnetoelectricity
Bousquet, Eric ULg; Spaldin, Nicola A; Delaney, Kris T

in Physical Review Letters (2011), 106(10),

We show that the electronic part of the linear magnetoelectric response, usually omitted in first-principles studies, can be comparable in magnitude to that mediated by polar lattice distortions, even in ... [more ▼]

We show that the electronic part of the linear magnetoelectric response, usually omitted in first-principles studies, can be comparable in magnitude to that mediated by polar lattice distortions, even in strong magnetoelectrics. Using a self-consistent response to a Zeeman field for noncollinear spins, we show how polarization emerges in magnetoelectrics through both electronic and lattice contributions-analogous to the high- and low-frequency responses of dielectrics. The approach we use is computationally simple, and can be used to study linear and nonlinear responses to magnetic fields. [less ▲]

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See detailElectrostriction at the LaAlO3/SrTiO3 Interface
Cancellieri, C.; Fontaine, Denis ULg; Gariglio, S. et al

in Physical Review Letters (2011), 107

We present a direct comparison between experimental data and ab initio calculations for the electrostrictive effect in the polar LaAlO3 layer grown on SrTiO3 substrates. From the structural data, a ... [more ▼]

We present a direct comparison between experimental data and ab initio calculations for the electrostrictive effect in the polar LaAlO3 layer grown on SrTiO3 substrates. From the structural data, a complete screening of the LaAlO3 dipole field is observed for film thicknesses between 6 and 20 uc. For thinner films, an expansion of the c axis of 2% matching the theoretical predictions for an electrostrictive effect is observed experimentally. [less ▲]

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See detailFirst glances at the transversity parton distribution through dihadron fragmentation functions
Bacchetta, A.; Courtoy, Aurore ULg; Radici, M.

in Physical Review Letters (2011), 107(1),

We present first observations of the transversity parton distribution based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. The extraction of ... [more ▼]

We present first observations of the transversity parton distribution based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. The extraction of transversity relies on the knowledge of dihadron fragmentation functions, which we take from electron-positron annihilation measurements. This is the first attempt to determine the transversity distribution in the framework of collinear factorization. © 2011 American Physical Society. [less ▲]

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See detailCompaction Dynamlics of Wet Granular Assemblies
Fiscina, J. E.; Lumay, Geoffroy ULg; Ludewig, François ULg et al

in Physical Review Letters (2010), 105

The extremely slow compaction dynamics of wet granular assemblies is studied experimentally. The cohesion, due to capillary bridges between neighboring grains, is tuned using different liquids having ... [more ▼]

The extremely slow compaction dynamics of wet granular assemblies is studied experimentally. The cohesion, due to capillary bridges between neighboring grains, is tuned using different liquids having specific surface tension values. The compaction dynamics of a cohesive packing obeys an inverse logarithmic law, like most dry random packings. However, the characteristic relaxation time 􏰌 grows strongly with cohesion. A model, based on free volume kinetic equations and the presence of a capillary energy barrier, is able to reproduce quantitatively the experimental curves. [less ▲]

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See detailStrain-induced ferroelectricity in simple rocksalt binary oxides
Bousquet, Eric ULg; Spaldin, N.; Ghosez, Philippe ULg

in Physical Review Letters (2010), 104

Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial ... [more ▼]

Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial strains. Going beyond the fundamental discovery, we highlight that the functional properties (polarization, dielectric constant, and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, making them of direct interest for applications. Finally, we show that magnetic binary oxides such as EuO, with the same rocksalt structure, behave similarly to the alkaline-earth-metal oxides, suggesting a route to new multiferroics combining ferroelectric and magnetic properties. [less ▲]

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See detailRegular-to-Chaotic Tunneling Rates: From the Quantum to the Semiclassical Regime
Loeck, Steffen; Baecker, Arnd; Ketzmerick, Roland et al

in Physical Review Letters (2010), 104(11), 114101

We derive a prediction of dynamical tunneling rates from regular to chaotic phase-space regions combining the direct regular-to-chaotic tunneling mechanism in the quantum regime with an improved resonance ... [more ▼]

We derive a prediction of dynamical tunneling rates from regular to chaotic phase-space regions combining the direct regular-to-chaotic tunneling mechanism in the quantum regime with an improved resonance-assisted tunneling theory in the semiclassical regime. We give a qualitative recipe for identifying the relevance of nonlinear resonances in a given h regime. For systems with one or multiple dominant resonances we find excellent agreement to numerics. [less ▲]

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See detailAsymmetric Optical Second-Harmonic Generation from Chiral G-Shaped Gold Nanostructures
Valev, V. K.; Silhanek, Alejandro ULg; Verellen, N. et al

in Physical Review Letters (2010), 104(12),

We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating ... [more ▼]

We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating the sample in an experiment involving solely linearly polarized light. This phenomenon originates in the surface plasmon resonance of chiral gold nanostructures, where homodyne interference of anisotropic and chiral electric and/or magnetic multipoles appears to play an important role. [less ▲]

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See detailFormation of Stripelike Flux Patterns Obtained by Freezing Kinematic Vortices in a Superconducting Pb Film
Silhanek, Alejandro ULg; Milosevic, M. V.; Kramer, R. B. G. et al

in Physical Review Letters (2010), 104(1),

We demonstrate experimentally and theoretically that the dissipative state of superconducting samples with a periodic array of holes at high current densities consists of flux rivers resulting from a ... [more ▼]

We demonstrate experimentally and theoretically that the dissipative state of superconducting samples with a periodic array of holes at high current densities consists of flux rivers resulting from a short-range attractive interaction between vortices. This dynamically induced vortex-vortex attraction results from the migration of quasiparticles out of the vortex core (kinematic vortices). We have directly visualized the formation of vortex chains by scanning Hall probe microscopy after freezing the dynamic state by a field cooling procedure at a constant bias current. Similar experiments carried out in a sample without holes show no hint of flux river formation. We shed light on this nonequilibrium phenomena modeled by time-dependent Ginzburg-Landau simulations. [less ▲]

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See detailLight-front interpretation of Proton Generalized Polarizabilities
Gorchtein, M.; Lorce, Cédric ULg; Pasquini, B. 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 ▲]

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See detailPhases of Polonium via Density Functional Theory
Verstraete, Matthieu ULg

in Physical Review Letters (2010), 104

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See detailRare-earth surface alloying: a new phase for GdAu$_2$
Corso, M.; Verstraete, Matthieu ULg; Schiller, F. et al

in Physical Review Letters (2010), 105

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See detailSemiclassical Gaps in the Density of States of Chaotic Andreev Billiards
Kuipers, Jack; Waltner, Daniel; Petitjean, Cyril ULg 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 ▲]

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See detailPolarization vortices in germanium telluride nanoplatelets: A theoretical study
Durgun, Engin ULg; Ghosez, Philippe ULg; Shaltaf, R. 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 ▲]

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See detailDynamics of the negative thermal expansion in tellurium based liquid alloys
Otjacques, C.; Raty, Jean-Yves ULg; Coulet, M-V 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 ▲]

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See detailSymmetry-Induced Giant Vortex State in a Superconducting Pb Film with a Fivefold Penrose Array of Magnetic Pinning Centers
Kramer, R. B. G.; Silhanek, Alejandro ULg; Van de Vondel, J. 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 ▲]

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See detailHow precisely will the total cross section be measured at the LHC?
Cudell, Jean-René ULg; Selyugin, O. V.

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 ▲]

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See detailOperational Families of Entanglement Classes for Symmetric N-Qubit States
Bastin, Thierry ULg; Krins, Stéphanie ULg; Mathonet, Pierre ULg 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 ▲]

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See detailOperational Determination of Multiqubit Entanglement Classes via Tuning of Local Operations
Bastin, Thierry ULg; Thiel, C.; von Zanthier, J. 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 ▲]

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See detailType-1.5 Superconductivity
Moshchalkov, Victor; Menghini, Mariela; Nishio, T. 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 ▲]

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