Transport, optical and electronic properties of the half metal CrO2

The electronic structure of CrO_2 is critically discussed in terms of the relation of existing experimental data and well converged LSDA and GGA calculations of the electronic structure and transport properties of this half metal magnet, with a particular emphasis on optical properties. We find only moderate manifestations of many body effects. Renormalization of the density of states is not large and is in the typical for transition metals range. We find substantial deviations from Drude behavior in the far-infrared optical conductivity. These appear because of the unusually low energy of interband optical transitions. The calculated mass renormalization is found to be rather sensitive to the exchange-correlation functional used and varies from 10% (LSDA) to 90% (GGA), using the latest specific heat data. We also find that dressing of the electrons by spin fluctuations, because of their high energy, renormalizes the interband optical transition at as high as 4 eV by about 20%. Although we find no clear indications of strong correlations of the Hubbard type, strong electron-magnon scattering related to the half metallic band structure is present and this leads to a nontrivial temperature dependence of the resistivity and some renormalization of the electron spectra.Comment: 9 Revtex 2 column pages, including 8 postscript figures. Two more figures are included in the submission that are not embedded in the paper, representing DOS and bandstructure of the paramagnetic CrO

Applications of high repetition rate tabletop soft X-ray lasers become a reality in several fields

Includes bibliographical references (page 468).For many years researchers have envisioned the development of compact high repetition rate tabletop soft x-ray laser, that could be routinely used in application in numerous disciplines. With demonstrated average powers of several mW and millijoule-level pulse energy at 46.9nm, the Ne-like Ar capillary discharge-pumped laser is the first compact laser to reach this goal. In this paper we summarize the development status of high repetition rate tabletop soft x-ray lasers based on capillary discharge excitation, and give examples of their successful use in several applications. Results of the use of a caprllary discharge pumped 46.9nm laser m dense plasma interferometry, soft x-ray reflectometry for the determination of optical constants, characterization of diffraction gratings, laser ablation of materials, and plasma generation are described. The observation of lasing at 52.9nm line in Ne-like Cl with output pulse energy up to 10 μJ is also reported

Continuous selections of multivalued mappings

This survey covers in our opinion the most important results in the theory of continuous selections of multivalued mappings (approximately) from 2002 through 2012. It extends and continues our previous such survey which appeared in Recent Progress in General Topology, II, which was published in 2002. In comparison, our present survey considers more restricted and specific areas of mathematics. Note that we do not consider the theory of selectors (i.e. continuous choices of elements from subsets of topological spaces) since this topics is covered by another survey in this volume

Effects of Crystal Structure and the On-Site Coulomb Interactions on the Electronic and Magnetic Structure of Pyrochlores A2A_2Mo2_2O7_7 (A= Y, Gd, and Nd)

Being motivated by recent experimental studies, we investigate magnetic structures of the Mo pyrochlores $A_2$Mo$_2$O$_7$ ($A$= Y, Nd, and Gd) and their impact on the electronic properties. The latter are closely related with the behavior of twelve Mo($t_{2g}$) bands, located near the Fermi level and well separated from the rest of the spectrum. We use a mean-field Hartree-Fock approach, which combines fine details of the electronic structure for these bands, extracted from the conventional calculations in the local-density approximation, the spin-orbit interaction, and the on-site Coulomb interactions amongst the Mo(4d) electrons, treated in the most general rotationally invariant form. The Coulomb repulsion U plays a very important role in the problem, and the semi-empirical value U$\sim$1.5-2.5 eV accounts simultaneously for the metal-insulator (M-I) transition, the ferromagnetic (FM) - spin-glass (SG) transition, and for the observed enhancement of the anomalous Hall effect (AHE). The M-I transition is mainly controlled by $U$. The magnetic structure at the metallic side is nearly collinear FM, due to the double exchange mechanism. The transition into the insulating state is accompanied by the large canting of spin and orbital magnetic moments. The sign of exchange interactions in the insulating state is controlled by the Mo-Mo distances. Smaller distances favor the antiferromagnetic coupling, which preludes the SG behavior in the frustrated pyrochlore lattice. Large AHE is expected in the nearly collinear FM state, near the point of M-I transition, and is related with the unquenched orbital magnetization at the Mo sites. We also predict large magneto-optical effect in the same FM compounds.Comment: 26 pages, 17 figures (low resolution is used for Figs. 6, 8, and 9, please contact directly if you need the originals), 1 tabl

Prediction of the atomic structure and stability for the ensemble of silicon nanoclusters passivated by hydrogen

The total energy and geometry of nanoclusters $\mathrm{Si}_{10}\mathrm{H}_{2m}\ (m=0\text{--}12)$ are calculated using evolutionary structure searching and density functional theory. The calculation shows that the arrangement of Si atoms is close to the diamond crystal structure only in the cluster $\mathrm{Si}_{10}\mathrm{H}_{16}$ , while in others it is unique for each composition. We found that the ensemble of $\mathrm{Si}_{10}$ clusters remains uniform after passivation only if hydrogen concentration corresponds to one of the stable compositions – $\mathrm{Si}_{10}$ , $\mathrm{Si}_{10}\mathrm{H}_{14}$ , $\mathrm{Si}_{10}\mathrm{H}_{16}\ \mathrm{Si}_{10}\mathrm{H}_{20}$ , or $\mathrm{Si}_{10}\mathrm{H}_{22}$ . Passivation by an arbitrary amount of hydrogen converts the ensemble into a mixture of the stable clusters having the nearest compositions. In addition there are numerous metastable cluster configurations with energies within $\sim0.1\ \text{eV}$ above the ground state. These metastable configurations come into existence in synthesis at $T\geq500\ \text{K}$ , making experimentally realizable cluster compositions even more diverse