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See detailUnveiling the Room-Temperature Magnetoelectricity of Troilite FeS
Ricci, Fabio ULg; Bousquet, Eric ULg

in Physical Review Letters (2016), 116

We report on a first-principles study of the troilite phase of iron sulfide (FeS). We show that even if, a few decades ago, this material was thought to be ferroelectric, the structural transition from ... [more ▼]

We report on a first-principles study of the troilite phase of iron sulfide (FeS). We show that even if, a few decades ago, this material was thought to be ferroelectric, the structural transition from the high P63/mmc to the low P6¯2c symmetry phase does not involve polar instabilities, though the space inversion center symmetry is broken. Our calculations and symmetry analysis nevertheless reveal that FeS is magnetoelectric at room temperature with a response larger than the prototypical room-temperature magnetoelectric crystal Cr2O3. We also show that the spin channel decomposition of the polarization exhibits nonzero values in the opposite direction in FeS, which is actually a general hint of the presence of a magnetoelectric monopole in diagonal magnetoelectrics. [less ▲]

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See detailElectric Field Control of Jahn-Teller Distortions in Bulk Perovskites
Varignon, Julien ULg; Bristowe, Nicholas ULg; Ghosez, Philippe ULg

in Physical Review Letters (2016), 116

The Jahn-Teller distortion, by its very nature, is often at the heart of the various electronic properties displayed by perovskites and related materials. Despite the Jahn-Teller mode being nonpolar, we ... [more ▼]

The Jahn-Teller distortion, by its very nature, is often at the heart of the various electronic properties displayed by perovskites and related materials. Despite the Jahn-Teller mode being nonpolar, we devise and demonstrate, in the present Letter, an electric field control of Jahn-Teller distortions in bulk perovskites. The electric field control is enabled through an anharmonic lattice mode coupling between the Jahn-Teller distortion and a polar mode. We confirm this coupling and quantify it through first-principles calculations. The coupling will always exist within the Pb21m space group, which is found to be the favored ground state for various perovskites under sufficient tensile epitaxial strain. Intriguingly, the calculations reveal that this mechanism is not only restricted to Jahn-Teller active systems, promising a general route to tune or induce novel electronic functionality in perovskites as a whole. [less ▲]

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See detailDisplacement of an Electrically Charged Drop on a Vibrating Bath
Brandenbourger, Martin ULg; Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in Physical Review Letters (2016), 116

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See detailStrain-Engineered Multiferroicity in Pnma NaMnF3 Fluoroperovskite
Garcia Castro, Andrés Camilo ULg; Bousquet, Eric ULg; Romero, Aldo H.

in Physical Review Letters (2016)

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See detailTensor Representation of Spin States
Giraud, Olivier; Braun, Daniel; Baguette, Dorian ULg et al

in Physical Review Letters (2015), 114

We propose a generalization of the Bloch sphere representation for arbitrary spin states. It provides a compact and elegant representation of spin density matrices in terms of tensors that share the most ... [more ▼]

We propose a generalization of the Bloch sphere representation for arbitrary spin states. It provides a compact and elegant representation of spin density matrices in terms of tensors that share the most important properties of Bloch vectors. Our representation, based on covariant matrices introduced by Weinberg in the context of quantum field theory, allows for a simple parametrization of coherent spin states, and a straightforward transformation of density matrices under local unitary and partial tracing operations. It enables us to provide a criterion for anticoherence, relevant in a broader context such as quantum polarization of light. [less ▲]

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See detailLow-Dimensional Transport and Large Thermoelectric Power Factors in Bulk Semiconductors by Band Engineering of Highly Directional Electronic States
Bilc, Daniel ULg; Hautier, Geoffroy; Waroquiers, David et al

in Physical Review Letters (2015), 114

Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but ... [more ▼]

Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but less by maximizing the power factor. The latter imposes apparently conflicting requirements on the band structure: a narrow energy distribution and a low effective mass. Quantum confinement in nanostructures andtheintroductionofresonantstatesweresuggestedaspossiblesolutionstothisparadox,butwithlimited success. Here, we propose an original approach to fulfill both requirements in bulk semiconductors. It exploits the highly directional character of some orbitals to engineer the band structure and produce a type of low-dimensional transport similar to that targeted in nanostructures, while retaining isotropic properties. Using first-principle calculations, the theoretical concept is demonstrated in Fe2YZ Heusler compounds, yielding power factors 4 to 5 times larger than in classical thermoelectrics at room temperature. Our findings are totally generic and rationalize the search of alternative compounds with similar behavior. Beyond thermoelectricity, these might be relevant also in the context of electronic, superconducting, or photovoltaic applications. [less ▲]

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See detailCoherent Electronic Wave Packet Motion in ${\mathrm{C}}_{60}$ Controlled by the Waveform and Polarization of Few-Cycle Laser Fields
Li, H.; Mignolet, Benoît ULg; Wachter, G. et al

in Physical Review Letters (2015), 114(12), 123004

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See detailBeyond-Standard-Model Tensor Interaction and Hadron Phenomenology
Courtoy, Aurore ULg; Baeßler, Stefan; González–Alonso, Martín et al

in Physical Review Letters (2015), 115(16), 162001

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See detailStrain Induced Vortex Core Switching in Planar Magnetostrictive Nanostructures
Ostler, Thomas ULg; Cuadrado, R.; Chantrell, R. W. et al

in Physical review letters (2015), 115(6), 067202

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See detailTwo Scenarios for Quantum Multifractality Breakdown
Dubertrand, Rémy ULg; Garcia-Mata, Ignacio; Georgeot, Bertrand et al

in Physical Review Letters (2014), 112

We expose two scenarios for the breakdown of quantum multifractality under the effect of perturbations. In the first scenario, multifractality survives below a certain scale of the quantum fluctuations ... [more ▼]

We expose two scenarios for the breakdown of quantum multifractality under the effect of perturbations. In the first scenario, multifractality survives below a certain scale of the quantum fluctuations. In the other one, the fluctuations of the wave functions are changed at every scale and each multifractal dimension smoothly goes to the ergodic value. We use as generic examples a one-dimensional dynamical system and the three-dimensional Anderson model at the metal-insulator transition. Based on our results, we conjecture that the sensitivity of quantum multifractality to perturbation is universal in the sense that it follows one of these two scenarios depending on the perturbation. We also discuss the experimental implications. [less ▲]

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See detailDynamics of a grain-filled ball on a vibrating plate
Pacheco Vazquez, Felipe ULg; Ludewig, François ULg; Dorbolo, Stéphane ULg

in Physical Review Letters (2014), 113

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See detailRole of disorder in the thermodynamics and atomic dynamics of glasses
Chumakov, A. I.; Monaco, G.; Fontana, A. et al

in Physical Review Letters (2014), 112(2),

We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat ... [more ▼]

We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal. © 2014 American Physical Society. [less ▲]

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See detailNuclear forward scattering of synchrotron radiation by Ru 99
Bessas, D.; Merkel, D. G.; Chumakov, A. I. et al

in Physical Review Letters (2014), 113(14),

We measured nuclear forward scattering spectra utilizing the Ru99 transition, 89.571(3) keV, with a notably mixed E2/M1 multipolarity. The extension of the standard evaluation routines to include mixed ... [more ▼]

We measured nuclear forward scattering spectra utilizing the Ru99 transition, 89.571(3) keV, with a notably mixed E2/M1 multipolarity. The extension of the standard evaluation routines to include mixed multipolarity allows us to extract electric and magnetic hyperfine interactions from Ru99-containing compounds. This paves the way for several other high-energy Mössbauer transitions, E∼90keV. The high energy of such transitions allows for operando nuclear forward scattering studies in real devices. © 2014 American Physical Society. [less ▲]

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See detailFirst Principles Explanation of the Positive Seebeck Coefficient of Lithium
Xu, Bin ULg; Verstraete, Matthieu ULg

in Physical Review Letters (2014), 112

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See detailAre Hydrogen-Bonded Charge Transfer Crystals Room Temperature Ferroelectrics?
D'Avino, Gabriele ULg; Verstraete, Matthieu ULg

in Physical Review Letters (2014), 113

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See detailCoherent Backscattering in Fock Space: A Signature of Quantum Many-Body Interference in Interacting Bosonic Systems
Engl, Thomas; Dujardin, Julien ULg; Argüelles, Arturo et al

in Physical Review Letters (2014), 112

We predict a generic signature of quantum interference in many-body bosonic systems resulting in a coherent enhancement of the average return probability in Fock space. This enhancement is robust with ... [more ▼]

We predict a generic signature of quantum interference in many-body bosonic systems resulting in a coherent enhancement of the average return probability in Fock space. This enhancement is robust with respect to variations of external parameters even though it represents a dynamical manifestation of the delicate superposition principle in Fock space. It is a genuine quantum many-body effect that lies beyond the reach of any mean-field approach. Using a semiclassical approach based on interfering paths in Fock space, we calculate the magnitude of the backscattering peak and its dependence on gauge fields that break time-reversal invariance. We confirm our predictions by comparing them to exact quantum evolution probabilities in Bose-Hubbard models, and discuss their relevance in the context of many-body thermalization. [less ▲]

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See detailDetecting transition radiation from a magnetic moment
Ivanov, Igor ULg; Karlovets, Dmitry

in Physical Review Letters (2013), 110(26), 2648015

Electromagnetic radiation can be emitted not only by particle charges but also by magnetic moments and higher electric and magnetic multipoles. However, experimental proofs of this fundamental fact are ... [more ▼]

Electromagnetic radiation can be emitted not only by particle charges but also by magnetic moments and higher electric and magnetic multipoles. However, experimental proofs of this fundamental fact are extremely scarce. In particular, the magnetic moment contribution has never been observed in any form of polarization radiation. Here, we propose to detect it using vortex electrons carrying large orbital angular momentum ℓ. The relative contribution of the orbital angular momentum-induced magnetic moment, ℓℏω/Ee, becomes much larger than the spin-induced contribution ℏω/Ee, and it can be observed experimentally. As a particular example, we consider transition radiation from vortex electrons obliquely incident on an interface between a vacuum and a dispersive medium, in which the magnetic moment contribution manifests itself via a left-right angular asymmetry. For electrons with Ee=300  keV and ℓ=100–1000, we predict an asymmetry of the order of 0.1%–1%, which could be measured with existing technology. Thus, vortex electrons emerge as a new tool in the physics of electromagnetic radiation. [less ▲]

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See detailComment on ``Proton Spin Structure from Measurable Parton Distributions''
Leader, Elliot; Lorce, Cédric ULg

in Physical Review Letters (2013), 111

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See detailTotal Current Blockade in an Ultracold Dipolar Quantum Wire
Kristinsdóttir, L.H.; Karlström, O.; Cremon, J.C. et al

in Physical Review Letters (2013), 110

Cold-atom systems offer a great potential for the future design of new mesoscopic quantum systems with properties that are fundamentally different from semiconductor nanostructures. Here, we investigate ... [more ▼]

Cold-atom systems offer a great potential for the future design of new mesoscopic quantum systems with properties that are fundamentally different from semiconductor nanostructures. Here, we investigate the quantum-gas analogue of a quantum wire and find a new scenario for the quantum transport: Attractive interactions may lead to a complete suppression of current in the low-bias range, a total current blockade. We demonstrate this effect for the example of ultracold quantum gases with dipolar interactions. [less ▲]

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See detailRole of Dynamical Instability in the Ab~Initio Phase Diagram of Calcium
Di Gennaro, Marco ULg; Saha, Srijan Kumar; Verstraete, Matthieu ULg

in Physical Review Letters (2013), 111

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