Electronic Structure of ZnCNi3

According to a recent report by Park et al, ZnCNi3 is isostructural and isovalent to the superconducting (Tc = 8 K) anti-perovskite, MgCNi3, but shows no indication of a superconducting transition down to 2K. A comparison of calculated electronic structures shows that the main features of MgCNi3, particularly the van Hove singularity near the Fermi energy, are preserved in ZnCNi3. Thus the reported lack of superconductivity in ZnCNi3 is not explainable in terms of Tc being driven to a very low value by a small Fermi level density of states. We propose that the lack of superconductivity, the small value of the linear specific heat coefficient, gamma, and the discrepancy between theoretical and experimental lattice constants can all be explained if the material is assumed to be a C-deficient alpha-ZnCNi3 similar to the analogous non-superconducting phase of MgCNi3

Origin of Tc Enhancement Induced by Doping Yttrium and Hydrogen into LaFeAsO-based Superconductors: 57Fe, 75As, 139La, and 1H-NMR Studies

We report our extensive 57Fe-, 75As-, 139La-, and 1H-NMR studies of La_{0.8}Y_{0.2}FeAsO_{1-y} (La_{0.8}Y_{0.2}1111) and LaFeAsO_{1-y}H_{x}(La1111H), where doping yttrium (Y) and hydrogen (H) into optimally doped LaFeAsO_{1-y} (La1111(OPT)) increases T_c=28 K to 34 and 32 K, respectively. In the superconducting (SC) state, the measurements of nuclear-spin lattice-relaxation rate 1/T_1 have revealed in terms of a multiple fully gapped s_\pm-wave model that the SC gap and T_c in La_{0.8}Y_{0.2}1111 become larger than those in La1111(OPT) without any change in doping level. In La1111H, the SC gap and T_c also increase slightly even though a decrease in carrier density and some disorders are significantly introduced. As a consequence, we suggest that the optimization of both the structural parameters and the carrier doping level to fill up the bands is crucial for increasing T_c among these La1111-based compounds through the optimization of the Fermi surface topology.Comment: 4 pages, 4 figures, 1 table, to be published in J. Phys. Soc. Jpn, Vol. 79, No. 1

Suppression of Magnetic Order by Pressure in BaFe2As2

We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2 under high pressure. The T-P phase diagram of BaFe2As2 determined from resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly is quite robust against P.Comment: 2 pages, 2 figure

Theoretical study of dislocation nucleation from simple surface defects in semiconductors

Large-scale atomistic calculations, using empirical potentials for modeling semiconductors, have been performed on a stressed system with linear surface defects like steps. Although the elastic limits of systems with surface defects remain close to the theoretical strength, the results show that these defects weaken the atomic structure, initializing plastic deformations, in particular dislocations. The character of the dislocation nucleated can be predicted considering both the resolved shear stress related to the applied stress orientation and the Peierls stress. At low temperature, only glide events in the shuffle set planes are observed. Then they progressively disappear and are replaced by amorphization/melting zones at a temperature higher than 900 K

On the Friedmann Equation in Brane-World Scenarios

The Friedmann law on the brane generically depends quadratically on the brane energy density and involves a ``dark radiation'' term due to the bulk Weyl tensor. Despite its unfamiliar form, we show how it can be derived from a standard four-dimensional Brans-Dicke theory at low energy. In particular, the dark radiation term is found to depend linearly on the brane energy densities. For any equation of state on the branes, the radion evolves such as to generate radiation-dominated cosmology. The radiation-dominated era is conventional and consistent with nucleosynthesis.Comment: 4 pages. v2,v3: discussion on BBN extended, minor correction

Alpha Decay Width of 212^{212}Po from a quartetting wave function approach

A microscopic calculation of $\alpha$-cluster preformation probability and $\alpha$ decay width in the typical $\alpha$ emitter $^{212}$Po is presented. Results are obtained by improving a recent approach to describe $\alpha$ preformation in $^{212}$Po [Phys. Rev. C 90, 034304 (2014)] implementing four-nucleon correlations (quartetting). Using the actually measured density distribution of the $^{208}$ Pb core, the calculated alpha decay width of $^{212}$Po agrees fairly well with the measured one.Comment: 7 pages, 5 figures, 1 table, submitted to Phys. Rev.

Ghost field realizations of the spinor W2,sW_{2,s} strings based on the linear W(1,2,s) algebras

It has been shown that certain W algebras can be linearized by the inclusion of a spin-1 current. This Provides a way of obtaining new realizations of the W algebras. In this paper, we investigate the new ghost field realizations of the W(2,s)(s=3,4) algebras, making use of the fact that these two algebras can be linearized. We then construct the nilpotent BRST charges of the spinor non-critical W(2,s) strings with these new realizations.Comment: 10 pages, no figure