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See detailCharge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism
Angst, M.; Hermann, Raphaël ULg; Christianson, A. D. 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 ▲]

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See detailTetrahedral clustering in molten lithium under pressure
Tamblyn, Isaac; Raty, Jean-Yves ULg; Bonev, Stanimir A.

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 ▲]

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See detailCharge Order, Dynamics, and Magnetostructural Transition in Multiferroic LuFe2O4
Xu, X. S.; Angst, M.; Brinzari, T. V. et al

in Physical Review Letters (2008), 101(22),

We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical and Mossbauer spectroscopies, magnetization, and x-ray scattering in order to understand the interplay between ... [more ▼]

We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical and Mossbauer spectroscopies, magnetization, and x-ray scattering in order to understand the interplay between charge, structure, and magnetism in this multiferroic material. We demonstrate that charge fluctuation has an onset well below the charge ordering transition, supporting the "order by fluctuation" mechanism for the development of charge order superstructure. Bragg splitting and large magneto-optical contrast suggest a low-temperature monoclinic distortion that can be driven by both temperature and magnetic field. [less ▲]

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See detailSuperfluidity versus Anderson localization in a dilute Bose gas
Paul, T.; Schlagheck, Peter ULg; Leboeuf, P. et al

in Physical Review Letters (2007), 98(21),

We consider the motion of a quasi-one-dimensional beam of Bose-Einstein condensed particles in a disordered region of finite extent. Interaction effects lead to the appearance of two distinct regions of ... [more ▼]

We consider the motion of a quasi-one-dimensional beam of Bose-Einstein condensed particles in a disordered region of finite extent. Interaction effects lead to the appearance of two distinct regions of stationary flow. One is subsonic and corresponds to superfluid motion. The other one is supersonic and dissipative and shows Anderson localization. We compute analytically the interaction-dependent localization length. We also explain the disappearance of the supersonic stationary flow for large disordered samples. [less ▲]

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See detailOrigin of reversed vortex ratchet motion
Gillijns, W.; Silhanek, Alejandro ULg; Moshchalkov, V. V. et al

in Physical Review Letters (2007), 99(24),

We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also ... [more ▼]

We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also essentially depends on the ratio between the characteristic interaction distance and the period of the asymmetric pinning potential. We study four samples with different periods d of the asymmetric potential. For large d the dc voltage V(dc) recorded under a ac excitation indicates that the average vortex drift is from bigger to smaller dots for all explored positive fields. As d is reduced, a series of sign reversals in the dc response are observed as a function of field. We show that the number of sign reversals increases as d decreases. These findings are in agreement with recent computer simulations and illustrate the relevance of the different characteristic lengths for the vortex rectification effects. [less ▲]

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See detailQuantum Imaging with Incoherent Photons
Thiel, C.; Bastin, Thierry ULg; Martin, John ULg et al

in Physical Review Letters (2007), 99

We propose a technique to obtain subwavelength resolution in quantum imaging with potentially 100% contrast using incoherent light. Our method requires neither path-entangled number states nor multiphoton ... [more ▼]

We propose a technique to obtain subwavelength resolution in quantum imaging with potentially 100% contrast using incoherent light. Our method requires neither path-entangled number states nor multiphoton absorption. The scheme makes use of N photons spontaneously emitted by N atoms and registered by N detectors. It is shown that for coincident detection at particular detector positions a resolution of lambda/N can be achieved. [less ▲]

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See detailDNA replication timing data corroborate in silico human replication origin predictions
Audit, B.; Nicolay, Samuel ULg; Huvet, M. et al

in Physical Review Letters (2007), 99

We develop a wavelet-based multiscale pattern recognition methodology to disentangle the replication- from the transcription-associated compositional strand asymmetries observed in the human genome ... [more ▼]

We develop a wavelet-based multiscale pattern recognition methodology to disentangle the replication- from the transcription-associated compositional strand asymmetries observed in the human genome. Comparing replication skew profiles to recent high-resolution replication timing data reveals that most of the putative replication origins that border the so-identified replication domains are replicated earlier than their surroundings whereas the central regions replicate late in the S phase. We discuss the implications of this first experimental confirmation of these replication origin predictions that are likely to be early replicating and active in most tissues. [less ▲]

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See detailGeneration of Symmetric Dicke States of Remote Qubits with Linear Optics
Thiel, C.; von Zanthier, J.; Bastin, Thierry ULg et al

in Physical Review Letters (2007), 99

We propose a method for generating all symmetric Dicke states, either in the long-lived internal levels of N massive particles or in the polarization degrees of freedom of photonic qubits, using linear ... [more ▼]

We propose a method for generating all symmetric Dicke states, either in the long-lived internal levels of N massive particles or in the polarization degrees of freedom of photonic qubits, using linear optical tools only. By means of a suitable multiphoton detection technique, erasing Welcher-Weg information, our proposed scheme allows the generation and measurement of an important class of entangled multiqubit states. [less ▲]

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See detailInclusion of Electric Octupole Contributions Explains the Fast Radiative Decays of Two Metastable States in Ar+
Lundin, P.; Gurell, J.; Norlin, L. O. et al

in Physical Review Letters (2007), 99

A laser probing investigation has yielded the lifetimes of the 3s23p41D3d 2G7=2;9=2 metastable doublet states of Ar. The results, obtained with the CRYRING ion storage ring of Stockholm, are 3:0 0:4 and 2 ... [more ▼]

A laser probing investigation has yielded the lifetimes of the 3s23p41D3d 2G7=2;9=2 metastable doublet states of Ar. The results, obtained with the CRYRING ion storage ring of Stockholm, are 3:0 0:4 and 2:1 0:1 s, respectively. Comparisons with theoretical values calculated with two independenttheoretical approaches, i.e., the pseudorelativistic Hartree-Fock method and the multiconfiguration Breit-Pauli approach, have allowed us to establish the unexpected and extraordinary strong contribution of an electric octupole (E3) transition to the ground state, in addition to the M1 decay channels to the 3d 2;4F states and the E2 contributions to the 4s 2P, 2D states. [less ▲]

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See detailCharge order superstructure with integer iron valence in Fe2OBO3
Angst, M.; Khalifah, P.; Hermann, Raphaël ULg et al

in Physical Review Letters (2007), 99(8),

Solution-grown single crystals of Fe2OBO3 were characterized by specific heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific heat at 340 K indicates the onset of charge order ... [more ▼]

Solution-grown single crystals of Fe2OBO3 were characterized by specific heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific heat at 340 K indicates the onset of charge order. Evidence for a doubling of the unit cell at low temperature is presented. Combining structural refinement of diffraction data and Mossbauer spectra, domains with diagonal charge order are established. Bond-valence-sum analysis indicates integer valence states of the Fe ions in the charge ordered phase, suggesting Fe2OBO3 is the clearest example of ionic charge order so far. [less ▲]

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See detailIncommensurate charge order phase in Fe2OBO3 due to geometrical frustration
Angst, M.; Hermann, Raphaël ULg; Schweika, W. et al

in Physical Review Letters (2007), 99(25),

The temperature dependence of charge order in Fe2OBO3 was investigated by resistivity and differential scanning calorimetry measurements, Mossbauer spectroscopy, and synchrotron x-ray scattering ... [more ▼]

The temperature dependence of charge order in Fe2OBO3 was investigated by resistivity and differential scanning calorimetry measurements, Mossbauer spectroscopy, and synchrotron x-ray scattering, revealing an intermediate phase between room temperature and 340 K, characterized by coexisting mobile and immobile carriers, and by incommensurate superstructure modulations with temperature-dependent propagation vector (1/2, 0, tau) . The incommensurate modulations arise from specific antiphase boundaries with low energy cost due to geometrical charge frustration. [less ▲]

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See detailDipole-induced vortex ratchets in superconducting films with arrays of micromagnets
de Souza Silva, C. C.; Silhanek, Alejandro ULg; Van de Vondel, J. et al

in Physical Review Letters (2007), 98(11),

We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and ... [more ▼]

We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by magnetic force microscopy imaging, the magnetic state of both systems can be adjusted to produce arrays of almost pointlike magnetic dipoles. By carrying out transport measurements with ac drive, we observed experimentally a recently predicted ratchet effect induced by the interaction between superconducting vortices and the magnetic dipoles. Moreover, we find that these magnetic textures produce vortex-antivortex patterns, which have a crucial role in the transport properties of this hybrid system. [less ▲]

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See detailDisplacement echoes: Classical decay and quantum freeze
Petitjean, Cyril ULg; Bevilaqua, Diego V.; Heller, Eric J. et al

in PHYSICAL REVIEW LETTERS (2007), 98(16), 164101-4

Motivated by neutron scattering experiments, we investigate the decay of the fidelity with which a wave packet is reconstructed by a perfect time-reversal operation performed after a phase-space ... [more ▼]

Motivated by neutron scattering experiments, we investigate the decay of the fidelity with which a wave packet is reconstructed by a perfect time-reversal operation performed after a phase-space displacement. In the semiclassical limit, we show that the decay rate is generically given by the Lyapunov exponent of the classical dynamics. For small displacements, we additionally show that, following a short-time Lyapunov decay, the decay freezes well above the ergodic value because of quantum effects. Our analytical results are corroborated by numerical simulations. [less ▲]

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See detailLaser steered ultrafast quantum dynamics of electrons in LiH.
Remacle, Françoise ULg; Nest, M.; Levine, R. D.

in Physical Review Letters (2007), 99(18), 183902

The response of the electronic system of LiH to a few-cycle strong field is computed by a time-dependent multiconfiguration method using a large, adaptive, basis set. The intensity, pulse duration ... [more ▼]

The response of the electronic system of LiH to a few-cycle strong field is computed by a time-dependent multiconfiguration method using a large, adaptive, basis set. The intensity, pulse duration, polarization, and phase of carrier frequency can all be tuned to steer the motion of the electrons. It is shown possible to, e.g., direct the electrons to move along the Li-H bond or normal to it. By shifting the phase, the electrons can be driven toward the Li nucleus or away from it. When the pulse is polarized not along the bond the result is a rotation of the charge density. [less ▲]

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See detailResonance-assisted decay of nondispersive wave packets
Wimberger, Sandro; Schlagheck, Peter ULg; Eltschka, Christopher et al

in Physical Review Letters (2006), 97(4),

We present a quantitative semiclassical theory for the decay of nondispersive electronic wave packets in driven, ionizing Rydberg systems. Statistically robust quantities are extracted combining resonance ... [more ▼]

We present a quantitative semiclassical theory for the decay of nondispersive electronic wave packets in driven, ionizing Rydberg systems. Statistically robust quantities are extracted combining resonance-assisted tunneling with subsequent transport across chaotic phase space and a final ionization step. [less ▲]

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See detailDirect experimental evidence for atomic tunneling of europium in crystalline Eu8Ga16Ge30
Hermann, Raphaël ULg; Keppens, Veerle; Bonville, Pierre et al

in Physical Review Letters (2006), 97(1),

Mossbauer-effect and microwave absorption experimental evidence unambiguously demonstrates the presence of slow, similar to 450 MHz, tunneling of magnetic europium between four equivalent sites in ... [more ▼]

Mossbauer-effect and microwave absorption experimental evidence unambiguously demonstrates the presence of slow, similar to 450 MHz, tunneling of magnetic europium between four equivalent sites in Eu8Ga16Ge30, a stoichiometric clathrate. Remarkably, six of the eight europium atoms, or 11% of the constituents in this solid, tunnel between these four sites separated by 0.55 angstrom. The off centering of the atoms or ions in crystalline clathrates appears to be a promising route for producing Rabi oscillators in solid-state materials. [less ▲]

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See detailQuantum reversibility and echoes in interacting systems
Petitjean, Cyril ULg; Jacquod, Ph

in PHYSICAL REVIEW LETTERS (2006), 97(12), 124103-4

In echo experiments, imperfect time-reversal operations are performed on a subset of the total number of degrees of freedom. To capture the physics of these experiments, we introduce a partial fidelity M ... [more ▼]

In echo experiments, imperfect time-reversal operations are performed on a subset of the total number of degrees of freedom. To capture the physics of these experiments, we introduce a partial fidelity M(B)(t), the Boltzmann echo, where only part of the system's degrees of freedom can be time reversed. We present a semiclassical calculation of M(B)(t). We show that, as the time-reversal operation is performed more and more accurately, the decay rate of M(B)(t) saturates at a value given by the decoherence rate of the controlled degrees of freedom due to their coupling to uncontrolled ones. We connect these results with NMR spin echo experiments. [less ▲]

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See detailLyapunov generation of entanglement and the correspondence principle
Petitjean, Cyril ULg; Jacquod, Ph

in PHYSICAL REVIEW LETTERS (2006), 97(19), 194103-4

We show how a classically vanishing interaction generates entanglement between two initially nonentangled particles, without affecting their classical dynamics. For chaotic dynamics, the rate of ... [more ▼]

We show how a classically vanishing interaction generates entanglement between two initially nonentangled particles, without affecting their classical dynamics. For chaotic dynamics, the rate of entanglement is shown to saturate at the Lyapunov exponent of the classical dynamics as the interaction strength increases. In the saturation regime, the one-particle Wigner function follows classical dynamics better and better as one goes deeper and deeper in the semiclassical limit. This demonstrates that quantum-classical correspondence at the microscopic level does not require coupling to a large number of external degrees of freedom. [less ▲]

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See detailIrreversible dynamics of the phase boundary in U(Ru(0.96)Rh(0.04))(2)Si(2) and implications for ordering
Silhanek, Alejandro ULg; Jaime, M.; Harrison, N. et al

in Physical Review Letters (2006), 96(13),

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru(0.96)Rh ... [more ▼]

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru(0.96)Rh(0.04))(2)Si(2), which yield irreversible properties similar to those at the valence transition of Yb(1-x)Y(x)InCu(4). To explain these similarities, we propose a bootstrap mechanism by which lattice parameter changes caused by an electric quadrupolar order parameter within phase II become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition. [less ▲]

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See detailNonlocal magnetic field-tuned quantum criticality in cubic CeIn3-xSnx (x=0.25)
Silhanek, Alejandro ULg; Ebihara, Takao; Harrison, N. et al

in Physical Review Letters (2006), 96(20),

We show that antiferromagnetism in lightly (approximate to 8%) Sn-doped CeIn3 terminates at a critical field mu H-0(c)=42 +/- 2 T. Electrical transport and thermodynamic measurements reveal the effective ... [more ▼]

We show that antiferromagnetism in lightly (approximate to 8%) Sn-doped CeIn3 terminates at a critical field mu H-0(c)=42 +/- 2 T. Electrical transport and thermodynamic measurements reveal the effective mass m(*) not to diverge, suggesting that cubic CeIn3 is representative of a critical spin-density wave (SDW) scenario, unlike the local quantum critical points reported in anisotropic systems such as CeCu6-xAux and YbRh2Si2-xGex. The existence of a maximum in m(*) at a lower field mu H-0(x)=30 +/- 1 T may be interpreted as a field-induced crossover from local moment to SDW behavior as the Neel temperature falls below the Fermi temperature. [less ▲]

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