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Kuchler R.,Max Planck Institute for Chemical Physics of Solids | Steinke L.,Max Planck Institute for Chemical Physics of Solids | Daou R.,Max Planck Institute for Chemical Physics of Solids | Daou R.,CNRS Crystallography and Material Science Laboratory | And 3 more authors.
Nature Materials | Year: 2014

Electron-like carriers in bismuth are described by the Dirac Hamiltonian, with a band mass becoming a thousandth of the bare electron mass along one crystalline axis. The existence of three anisotropic valleys offers electrons an additional degree of freedom, a subject of recent attention. Here, we map the Landau spectrum by angle-resolved magnetostriction, and quantify the carrier number in each valley: while the electron valleys keep identical spectra, they substantially differ in their density of states at the Fermi level. Thus, the electron fluid does not keep the rotational symmetry of the lattice at low temperature and high magnetic field, even in the absence of internal strain. This effect, reminiscent of the Coulomb pseudogap in localized electronic states, affects only electrons in the immediate vicinity of the Fermi level. It presents the most striking departure from the non-interacting picture of electrons in bulk bismuth. © 2014 Macmillan Publishers Limited. Source

Raveau B.,CNRS Crystallography and Material Science Laboratory
Angewandte Chemie - International Edition | Year: 2013

Transition-metal oxides have been widely studied for understanding the physics of strongly electron-correlated systems. The crucial role of crystal chemistry for the discovery of three families: the high Tc superconducting cuprates, the colossal magnetoresistance manganates, the thermoelectric, and multiferroic cobaltates, is explored. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Juillet O.,University of Caen Lower Normandy | Fresard R.,CNRS Crystallography and Material Science Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Intertwining of spin, charge, and pairing correlations in the repulsive two-dimensional Hubbard model is shown through unrestricted variational calculations, with projected wave functions free of symmetry breaking. A crossover from incommensurate antiferromagnetism to stripe order naturally emerges in the hole-doped region when increasing the on-site coupling. Although effective attractive pairing interactions are identified, they are strongly fragmented in several modes including d-wave pairing and more exotic channels related to an underlying stripe. We demonstrate that the entanglement of a mean-field wave function by symmetry restoration can largely account for interaction effects, and that our approach is exact for a two-site cluster. © 2013 American Physical Society. Source

Raveau B.,CNRS Crystallography and Material Science Laboratory
Comptes Rendus Chimie | Year: 2011

Transition metal oxides represent a vast field for the study of strongly correlated electron systems, at the interface of crystal chemistry and physics. We describe herein the factors which govern the magnetic and transport properties of several families of oxides, which are promising functional materials: high TC superconductive cuprates, colossal magnetoresistance (CMR) manganites, thermoelectric cobaltites and multiferroic perovskites. © 2011 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved. Source

Meher K.R.S.P.,CNRS Crystallography and Material Science Laboratory | Martin C.,CNRS Crystallography and Material Science Laboratory | Caignaert V.,CNRS Crystallography and Material Science Laboratory | Damay F.,CEA Saclay Nuclear Research Center | Maignan A.,CNRS Crystallography and Material Science Laboratory
Chemistry of Materials | Year: 2014

Oxides containing magnetic 3d transition metals offer a large family of structures with frustrated magnetic networks. Some of those incommensurate antiferromagnetic structures are responsible for the local breaking of inversion symmetry so that these oxides are called spin-induced ferroelectrics. As listed in the introduction of this short review, the number of these multiferroics continues to increase. As for applications, the coupling between these ferroisms is needed; some magnetic oxides, despite a lack of ferroelectric ground state, exhibit large magnetoelectric coupling with a magnetic-field-induced polarization. Thus, they are classified as "magnetoelectrics". In the present review, we focus on recently studied systems showing ferroelectric-like behaviors or large magnetoelectric coefficients. This will be illustrated by chromites with the comparison between ceramics of CuCrO2 and AgCrS2: they exhibit different antiferromagnetic ground states, centrosymmetric and noncentrosymmetric. For the magnetoelectrics, the example of the cobaltite, CaBaCo4O7, which is a polar ferrimagnet, is taken to illustrate the existence of large magnetoelectric coefficients in crystals. Then, the existence of spin-induced ferroelectricity in centrosymmetric orthochromites (RECrO3 with RE = Lu or Er) is discussed. Through this selection of potential multiferroics or magnetoelectrics, it is clear that many magnetic materials in different forms (bulk/crystal/thin film) remain to be studied. © 2013 American Chemical Society. Source

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