28,571 research outputs found
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 Po from a quartetting wave function approach
A microscopic calculation of -cluster preformation probability and
decay width in the typical emitter Po is presented.
Results are obtained by improving a recent approach to describe
preformation in Po [Phys. Rev. C 90, 034304 (2014)] implementing
four-nucleon correlations (quartetting). Using the actually measured density
distribution of the Pb core, the calculated alpha decay width of
Po agrees fairly well with the measured one.Comment: 7 pages, 5 figures, 1 table, submitted to Phys. Rev.
<i>M</i><sup>2</sup>-MedDialog: A Dataset and Benchmarks for Multi-domain Multi-service Medical Dialogues
Ghost field realizations of the spinor 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
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