1,721,019 research outputs found
Determination of local distortions in the charge ordered and CMR La1-xCaxMnO3 manganites
No full textThe strain of CuO2 lattice: the second variable for the phase diagram of cuprate perovskites
No full textGiuseppe Alberigo (éd.), Conciliorum Oecumenicorum Generaliumque Decreta. Editio Critica. I, The Oecumenical Councils. From Nicaea I To Nicaea II (325-787). Curantibus G. Alberigo, A. M. Ritter, L. Abramowski, E. Mühlenberg, P. Conte, H.-G. Thümmel, G. Nedungatt, S. Agrestini, E. Lamberz, J. B. Uphus
No full textFailler Albert. Giuseppe Alberigo (éd.), Conciliorum Oecumenicorum Generaliumque Decreta. Editio Critica. I, The Oecumenical Councils. From Nicaea I To Nicaea II (325-787). Curantibus G. Alberigo, A. M. Ritter, L. Abramowski, E. Mühlenberg, P. Conte, H.-G. Thümmel, G. Nedungatt, S. Agrestini, E. Lamberz, J. B. Uphus. In: Revue des études byzantines, tome 66, 2008. pp. 259-260
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Common features in high Tc cuprates and diborides
No full textThe features of the normal state of cuprate superconductors, that drive up the Tc from the low temperature range TcTbH, i.e., the “smoking gun” for the “high-Tc” has not been found even after 18 years from the discovery of the superconductivity in these complex doped Mott insulators. Magnesium diboride provides a superconductor with Tc>TbH that has a normal phase well described by the standard solid state theory. Therefore it provides the simplest system for the “high Tc superconductivity” as the atomic hydrogen was the simplest system for the “quantum mechanics”. Here we show that the normal state of the magnesium diboride shows key features, that are in common with cuprates, and shed light on the pairing mechanism for Tc amplification in the high-Tc superconductors
A quantum phase transition driven by the electron lattice interaction gives high Tc superconductivity
No full textWe identify for the first time the quantum phase transition (QPT) as a function of the electron lattice interaction for charge localization in stripes with local lattice distortions in cuprate perovskites at metallic densities. The electron lattice interaction lambda(eta) is triggered at the localization limit by the strain eta of the CuO2 plane due to the chemical pressure generated by the mismatch between the copper oxide and the rocksalt layers. The strain of the CuO2 plane has been directly measured by Cu K-edge EXAFS. The critical point for the ch;uge localization in striped lattice domains coexisting with itinerant carriers is at eta (c)=0.04 +/-0.005 and delta (c)=0.16 +/-0.03. We report a 2D plot T-c (delta,eta) for the doped perovskites, where delta is the doping. The plot T-c(eta), for delta =constant, shows the highest T-c at the critical point eta (c)=0.04 +/-0.01. The attractive pseudo Jahn-Teller (pJT) interaction and the particular critical charge and spin fluctuations driven by critical ordering of cooperative pJT local lattice distortions, forming a superlattice of quantum stripes tuned at a 'shape resonance' near this quantum critical point, provide a possible solution for two long standing mysteries: the phase diagram and the pairing mechanism in cuprate superconducters
Resonant X-ray scattering study of Ca3Co2O6 ground state: Preliminary results of magnetic field effects
No full textWe present resonant magnetic X-ray scattering (RMXS) measurements in an applied magnetic field on a single crystal of Ca3Co2O6. We focus our attention on the transition from an incommensurate partially disordered antiferromagnetic state to a ferrimagnetic state: a lock-in and a divergence of the magnetic correlation length at the transition shed light on the nature of the ground state and on the c-axis vs. in-plane exchange couplings in this system. (C) 2009 Elsevier B.V. All rights reserved
Resonant x-ray scattering investigation of the multipolar ordering in Ca3Co2O6
No full textWe have performed a resonant x-ray scattering (RXS) study near the Co K edge on a single crystal of Ca3Co2O6. In the magnetically ordered phase a new class of weak reflections appears at the magnetic propagation vector (tau) over right arrow similar or equal to(1/3,1/3,1/3). These new reflections allow direct access to the dipolar-quadrupolar E1E2 scattering channel. The theoretical possibility of observing isolated E1E2 electromagnetic multipoles has attracted a lot of interest in recent years. Unfortunately in many systems of interest, parity even and parity odd tensor contributions occur at the same positions in reciprocal space. We demonstrate that in Ca3Co2O6 it is possible to completely separate the parity even from the parity odd terms. The possibility of observing such terms even in globally centrosymmetric systems using RXS has been investigated theoretically; Ca3Co2O6 allows a symmetry based separation of this contribution
Incommensurate magnetic ground state revealed by resonant x-ray scattering in the frustrated spin system Ca3Co2O6
No full textWe have performed a resonant x-ray scattering study at the Co pre-K edge on a single crystal of Ca3Co2O6. The measurements reveal an abrupt transition to a magnetically ordered state immediately below T-N=25 K, with a magnetic correlation length in excess of 5500 A along the c axis chains. There is no evidence for modifications to the Co3+ spin state. A temperature dependent modulation in the magnetic order along the c axis and an unusual decrease in the magnetic correlation lengths on cooling are observed. The results are compatible with the onset of a partially disordered antiferromagnetic structure in Ca3Co2O6
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