LaFeAsO1−x_{1-x}Fx_x: A low carrier density superconductor near itinerant magnetism

Density functional studies of 26K superconducting LaFeAs(O,F) are reported. We find a low carrier density, high density of states, $N(E_F)$ and modest phonon frequencies relative to $T_c$. The high $N(E_F)$ leads to proximity to itinerant magnetism, with competing ferromagnetic and antiferromagnetic fluctuations and the balance between these controlled by doping level. Thus LaFeAs(O,F) is in a unique class of high $T_c$ superconductors: high $N(E_F)$ ionic metals near magnetism.Comment: Shortened published form. Typos correcte

Density functional study of FeS, FeSe and FeTe: Electronic structure, magnetism, phonons and superconductivity

We report density functional calculations of the electronic structure, Fermi surface, phonon spectrum, magnetism and electron-phonon coupling for the superconducting phase FeSe, as well as the related compounds FeS and FeTe. We find that the Fermi surface structure of these compounds is very similar to that of the Fe-As based superconductors, with cylindrical electron sections at the zone corner, cylindrical hole surface sections, and depending on the compound, other small hole sections at the zone center. As in the Fe-As based materials, these surfaces are separated by a 2D nesting vector at ($\pi$,$\pi$). The density of states, nesting and Fermi surface size increase going from FeSe to FeTe. Both FeSe and FeTe show spin density wave ground states, while FeS is close to an instability. In a scenario where superconductivity is mediated by spin fluctuations at the SDW nesting vector, the strongest superconductor in this series would be doped FeTe.Comment: Added note regarding recent experimental observations of superconductivity under pressure. Some additional discussio

Electronic Structure and Thermoelectric Prospects of Phosphide Skutterudites

The prospects for high thermoelectric performance in phosphide skutterudites are investigated based on first principles calculations. We find that stoichiometric CoP_3 differs from the corresponding arsenide and antimonide in that it is metallic. As such the band structure must be modified if high thermopowers are to be achieved. In analogy to the antimonides it is expected that this may be done by filling with La. Calculations for LaFe_4P_12 show that a gap can in fact be opened by La filling, but that the valence band is too light to yield reasonable p-type thermopowers at appropriate carrier densities; n-type La filled material may be more favorable.Comment: 3 pages, 3 figures, 1 tabl

Layered Kondo lattice model for quantum critical beta-YbAlB4

We analyze the magnetic and electronic properties of the quantum critical heavy fermion superconductor beta-YbAlB4, calculating the Fermi surface and the angular dependence of the extremal orbits relevant to the de Haas--van Alphen measurements. Using a combination of the realistic materials modeling and single-ion crystal field analysis, we are led to propose a layered Kondo lattice model for this system, in which two dimensional boron layers are Kondo coupled via interlayer Yb moments in a $J_{z}=\pm 5/2$ state. This model fits the measured single ion magnetic susceptibility and predicts a substantial change in the electronic anisotropy as the system is pressure-tuned through the quantum critical point.Comment: Fig.3 and 4 have been updated, typos corrected in v2. Published at http://link.aps.org/doi/10.1103/PhysRevLett.102.07720

Null Geodesic Expansion in Spherical Gravitational Collapse

We derive an expression for the expansion of outgoing null geodesics in spherical dust collapse and compute the limiting value of the expansion in the approach to singularity formation. An analogous expression is derived for the spherical collapse of a general form of matter. We argue on the basis of these results that the covered as well as the naked singularity solutions arising in spherical dust collapse are stable under small changes in the equation of state.Comment: 10 pages, Latex File, No figure

Study on Genetic Variability, Heritability, Genetic Advance and Correlation among different characters in tomato (Solanum lycopersicum L.)

The present investigation entitled “Studies on genetic variability in tomato (Solanum lycopersicum L.)” was carried out at the UCOA, vegetable research farm, Guru Kashi University, Talwandi Sabo, Bathinda during rabi 2015-16 to evaluate tomato genotypes. The experiment was laid out in CRD with three replications. Total 20 genotypes including check cultivar were evaluated for horticultural Traits contributing yield and quality (suitable for processing) .There is a wide variability in different genotypes in tomato. Traits i.e. Number of primary branches per plant, Days to first fruit harvest, Plant height (cm),number of fruits per cluster, number fruits per plant, average fruit weight (gm), equatorial diameter of fruit (cm), polar diameter of fruit (cm), number of locules per fruit, pericarp thickness (mm), fruit pH, Fruit TSS (0brix), days to last fruit harvest and average yield per plant (kg) were studied during the investigation Analysis of variance showed significant differences among genotypes for all the characters under study during the investigation. High Phenotypic and Genotypic coefficient of variation were detected for characters like number of fruits per plant, number of locules per fruit, pericarp thickness and average yield per plant. High heritability coupled with genetic gain were recorded for number of fruits per plant, average fruit weight, number of locules per fruit and average yield per plant. Therefore these characters also show some scope for improvement through selection. A highly significant and positive phenotypic and genotypic correlation were found in number of fruits per cluster, plant height, number of fruits per plant and average fruit weight

The second phase transition in the pyrochlore oxide Cd2Re2O7

Evidence for another phase transition at 120 K in the metallic pyrochlore oxide Cd2Re2O7, following the structural transition at 200 K and followed by the superconducting transition at 1.0 K, is given through resistivity, magnetoresistance, specific heat, and X-ray diffraction measurements. The results indicate unique successive structural and electronic transitions occurring in the pyrochlore compound, revealing an interesting interplay between the crystal and electronic structures on the itinerant electron system in the pyrochlore lattice