1,654 research outputs found
Polaronic metal state at the LaAlO₃/SrTiO₃ interface
No full textInterplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures
Comment on Rogalev et al. Structural and Parametric Optimization of S-CO2 Thermal Power Plants with a Pulverized Coal-Fired Boiler Operating in Russia. Energies 2021, 14, 7136
No full textThe reconstruction of ageing thermal power plants with the possibility of their increased efficiency, prolonged service and decreased environmental impact is an intensely debated and researched topic nowadays. Among various concepts, the replacement of the steam cycle by a supercritical CO2 cycle is proposed with the prospect of reaching higher efficiencies at the same working fluid inlet parameters as the ultra-supercritical steam cycles. A paper published previously by Rogalev et al. (2021) analyzed the variants of supercritical coal power plant reconstruction to a supercritical CO2 cycle and ranked them according to the cycle efficiency. This contribution comments on the scope and applied method in that paper aiming to provide additional input relevant to the decision-making process on thermal power plant reconstruction to such a cycle
X-ray Optical Activity: Applications of Sum Rules
No full textEdge-selective sum rules are proposed for a variety of X-ray dichroisms related to natural or non- reciprocal optical activity. Four spherical operators are identified that mix orbitals of different parities in what is assumed to be the ground state. The orbital anapole moment W(1) is primarily responsible for the magne- tochiral dichroism; the time-even rank-2 tensor N(2) = [L, W](2) for natural circular dichroism; the time-odd rank-2 tensor W(2) = [L, n](2) for nonreciprocal magnetic linear dichroisms. At higher orders, the time-odd rank- 3 tensor G(3) = [L, L, W](3) can also contribute to all nonreciprocal dichroisms. The physical content of these operators is analyzed. For every magnetoelectric group, one can predict which dichroic effect can be measured with either a single crystal or a powdered sample. Experimental spectra are produced to illustrate the value of the sum rules and the practical conditions of their application. Regarding nonreciprocal activity, one should be
cautious about discussing magnetic symmetry because the deep core hole can couple the true ground state with low-lying excited states
Local noncentrosymmetric structure of Bi2Sr2CaCu2O8+y by X-ray magnetic circular dichroism at Cu K-edge XANES
No full textThe two-dimensional Bi2Sr2CaCu2O8+y (Bi2212), the most studied prototype cuprate superconductor, is a lamellar system made of a stack of two-dimensional corrugated CuO2 bilayers separated by Bi2O2+y Sr2O2 layers. While the large majority of theories, proposed to interpret unconventional high Tc superconductivity in Bi2Sr2 CaCu2O8+y, assume a centrosymmetric tetragonal CuO2 lattice for the [CuO2]Ca[CuO2] bilayer, here, we report new compelling results providing evidence for local noncentrosymmetric symmetry at the Cu atom. We have measured polarized Cu K-edge XANES (X-ray absorption near-edge structure) and the K-edge X-ray magnetic circular dichroism (XMCD) of a Bi2212 single-crystal near-optimum doping. The Cu K-edge XMCD signal was measured at ID12 beamline of ESRF with the k-vector of X-ray beam parallel to c-axis, i.e., with the electric field of X-ray beam E//ab, using a 17-T magnetic field parallel to the c-axis of a Bi2212 single crystal. Numerical simulations of the XMCD signal of Bi2212 by multiple scattering theory have shown agreement with the experimental XMCD signal only for the local structure with noncentrosymmetric Bb2b space group of Bi2Sr2CaCu2O8+y
Kinetic data for the article "Understanding the Reversible and Irreversible Deactivation of Methane Oxidation Catalysts" Applied Catalysis B: Environment and Energy, 123646
No full textSupporting information to the article "Understanding the Reversible and Irreversible Deactivation of Methane Oxidation Catalysts" by Rasmus Lykke Mortensen,[a,b] Hendrik-David Noack[b], Kim Pedersen,[b] Maja A. Dunstan,(a) Fabrice Wilhelm,(c) Andrei Rogalev,(c) Kasper S. Pedersen,(a)Jerrik Mielby*[a] and Susanne Mossin*[a][a] R. L. Mortensen, Prof. S. Mossin, and Dr. J. Mielby, DTU Chemistry, Technical University of Denmark, Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark, [email protected][b] H.-D. Noack, Dr. K. Pedersen, Umicore Denmark Aps, Kogle Allé 1, DK-2970 Hørsholm, Denmark[c] Dr. Fabrice Wilhelm, Dr. Andrei Rogalev, ESRF – The European Synchrotron, BP 220, 38043 Grenoble Cedex 9, France.</p
Ce 5d Magnetic Profile in Fe/Ce Multilayers for the a and g-like Ce phase by X-Ray Resonant Magnetic Scattering
No full textThe in-depth distribution of the induced 5d magnetic moments across the Ce layers in Fe/Ce/La/Ce, Fe/La/Ce/La and Fe/CeH2-delta multilayers has been investigated by x-ray resonant magnetic scattering (XRMS) at the Ce L-2 edge. The determination of the composition profile across the period of the multilayer is required for a quantitative analysis of XRMS and has been derived from x-ray resonant reflectivity measurements. In Fe/Ce/La/Ce and Fe/La/Ce/La multilayers, Ce adopts an alpha-like electronic configuration and the local magnetization, across the Ce layer, is found to be highly nonuniform. The Ce 5d magnetic profile shows an oscillating behavior with an amplitude decreasing from the Fe interface in Fe/Ce/La/Ce. Conversely, in Fe/La/Ce/La, where the Ce atoms are not in direct contact with Fe atoms, it presents an oscillatory profile with, however, a nearly constant amplitude. In Fe/CeH2-delta multilayers, where hydrogen leads to a strain relaxation and to a 4f relocalization (Ce gamma-like configuration), a nonoscillating decreasing profile has been observed. These experiments allow one to evidence an antiferromagnetic component in a alpha Ce ultrathin layer and a sharply decreasing induced magnetization due to 5d-3d hybridization at the interface
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