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See detailHighly Confined Spin-Polarized Two-Dimensional Electron Gas in SrTiO3/SrRuO3 Superlattices
Verissimo-Alves, M.; Garcia-Fernandez, P.; Bilc, Daniel ULg et al

in Physical Review Letters (2012), 108

We report first-principles characterization of the structural and electronic properties of (SrTiO3)5/(SrRuO3)1 superlattices. We show that the system exhibits a spin-polarized two-dimensional electron gas ... [more ▼]

We report first-principles characterization of the structural and electronic properties of (SrTiO3)5/(SrRuO3)1 superlattices. We show that the system exhibits a spin-polarized two-dimensional electron gas, extremely confined to the 4d orbitals of Ru in the SrRuO3 layer. Every interface in the superlattice behaves as a minority-spin half-metal ferromagnet, with a magnetic moment of µ = 2.0µB/SrRuO3 unit. The shape of the electronic density of states, half-metallicity, and magnetism are explained in terms of a simplified tight-binding model, considering only the t2g orbitals plus (i) the bidimensionality of the system and (ii) strong electron correlations. [less ▲]

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See detailInterplay between Nonequilibrium and Equilibrium Spin Torque Using Synthetic Ferrimagnets
Klein, Christian; Petitjean, Cyril ULg; Waintal, Xavier

in PHYSICAL REVIEW LETTERS (2012), 108(8), 086601-5

We discuss the current induced magnetization dynamics of spin valves F-0 vertical bar N vertical bar SyF where the free layer is a synthetic ferrimagnet SyF made of two ferromagnetic layers F-1 and F-2 ... [more ▼]

We discuss the current induced magnetization dynamics of spin valves F-0 vertical bar N vertical bar SyF where the free layer is a synthetic ferrimagnet SyF made of two ferromagnetic layers F-1 and F-2 coupled by RKKY exchange coupling. When the magnetic moment of the outer layer F-2 dominates the magnetization of the SyF, the sign of the effective spin torque exerted on the layer F-1 is controlled by the coupling's strength: for weak coupling the spin torque tends to antialign F-1's magnetization with respect to the pinned layer F-0. At large coupling the situation is reversed and tends to align F-1 with respect to F-0. At intermediate coupling, numerical simulations reveal that the competition between these two incompatible limits leads generically to spin torque oscillator (STO) behavior. The STO is found at zero magnetic field, with very significant amplitude of oscillations and frequencies up to 50 GHz or higher. [less ▲]

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See detailUnified Drift-Diffusion Theory for Transverse Spin Currents in Spin Valves, Domain Walls, and Other Textured Magnets
Petitjean, Cyril ULg; Luc, David; Waintal, Xavier

in PHYSICAL REVIEW LETTERS (2012), 109(11), 117204-5

Spins transverse to the magnetization of a ferromagnet only survive over a short distance. We develop a drift-diffusion approach that captures the main features of transverse spin effects in systems with ... [more ▼]

Spins transverse to the magnetization of a ferromagnet only survive over a short distance. We develop a drift-diffusion approach that captures the main features of transverse spin effects in systems with arbitrary spin textures (e.g., vortices and domain walls) and generalizes the Valet-Fert theory. In addition to the standard characteristic lengths (mean free path for majority and minority electrons, and spin diffusion length), the theory introduces two length scales, the transverse spin coherence length l(perpendicular to) and the (Larmor) spin precession length l(L). We show how l(L) and l(perpendicular to) can be extracted from ab initio calculations or measured with giant magnetoresistance experiments. In long (adiabatic) domain walls, we provide an analytic formula that expresses the so-called "nonadiabatic" (or fieldlike) torque in terms of these length scales. However, this nonadiabatic torque is no longer a simple material parameter but depends on the actual spin texture: in thin (< 10 nm) domain walls, we observe very significant deviations from the adiabatic limit. [less ▲]

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See detailSpontaneous 2-Dimensional Carrier Confinement at the n-Type SrTiO3=LaAlO3 Interface
Delugas, P.; Filippetti, A.; Fiorentini, V. et al

in Physical Review Letters (2011), 106

We describe the intrinsic mechanism of 2-dimensional electron confinement at the n-type SrTiO3=LaAlO3 interface as a function of the sheet carrier density ns via advanced first-principles calculations ... [more ▼]

We describe the intrinsic mechanism of 2-dimensional electron confinement at the n-type SrTiO3=LaAlO3 interface as a function of the sheet carrier density ns via advanced first-principles calculations. Electrons localize spontaneously in Ti 3dxy levels within a thin (& 2 nm) interface-adjacent SrTiO3 region for ns lower than a threshold value nc 1014 cm 2. For ns >nc a portion of charge flows into Ti 3dxz-dyz levels extending farther from the interface. This intrinsic confinement can be attributed to the interface-induced symmetry breaking and localized nature of Ti 3d t2g states. The sheet carrier density directly controls the binding energy and the spatial extension of the conductive region. A direct, quantitative relation of these quantities with ns is provided. [less ▲]

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See detailStabilization of Nonclassical States of the Radiation Field in a Cavity by Reservoir Engineering
Sarlette, Alain ULg; Raimond, Jean-Michel; Brune, Michel et al

in Physical Review Letters (2011), 107

We propose an engineered reservoir inducing the relaxation of a cavity field towards nonclassical states. It is made up of two-level atoms crossing the cavity one at a time. Each atom-cavity interaction ... [more ▼]

We propose an engineered reservoir inducing the relaxation of a cavity field towards nonclassical states. It is made up of two-level atoms crossing the cavity one at a time. Each atom-cavity interaction is first dispersive, then resonant, then dispersive again. The reservoir pointer states are those produced by an effective Kerr Hamiltonian acting on a coherent field. We thereby stabilize squeezed states and quantum superpositions of multiple coherent components in a cavity having a finite damping time. This robust decoherence protection method could be implemented in state-of-the-art experiments. [less ▲]

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See detailVortex Core Deformation and Stepper-Motor Ratchet Behavior in a Superconducting Aluminum Film Containing an Array of Holes
Van de Vondel, J.; Gladilin, V. N.; Silhanek, Alejandro ULg et al

in Physical Review Letters (2011), 106(13),

We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time-dependent ... [more ▼]

We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time-dependent Ginzburg-Landau formalism. We demonstrate that the high frequency vortex behavior can be described as a discrete motion of a particle in a periodic potential, i.e., the so-called stepper-motor behavior. Strikingly, in the more conventional low frequency response a transition takes place from an Abrikosov vortex rectifier to a phase slip line rectifier. This transition is characterized by a strong increase in the rectified voltage and the appearance of a pronounced hysteretic behavior. [less ▲]

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See detailInduced Magnetoelectric Response in Pnma Perovskites
Bousquet, Eric ULg; Spaldin, Nicola

in Physical Review Letters (2011), 107(19),

We use symmetry analysis to show that the G-, C-, and A-type antiferromagnetic Pnma perovskites can exhibit magnetoelectric (ME) responses when a ferroelectric instability is induced with epitaxial strain ... [more ▼]

We use symmetry analysis to show that the G-, C-, and A-type antiferromagnetic Pnma perovskites can exhibit magnetoelectric (ME) responses when a ferroelectric instability is induced with epitaxial strain. Using first-principles calculations we compute the values of the allowed ME response in strained CaMnO(3) as a model system. Our results show that large linear and non-linear-ME responses are present and can diverge when close to the ferroelectric phase transition. By decomposing the electronic and ionic contributions, we explore the detailed mechanism of the ME response. [less ▲]

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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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