29,040 research outputs found
Quantum Spin Chain, Toeplitz Determinants and Fisher-Hartwig Conjecture
We consider one-dimensional quantum spin chain, which is called XX model, XX0
model or isotropic XY model in a transverse magnetic field. We study the model
on the infinite lattice at zero temperature. We are interested in the entropy
of a subsystem [a block of L neighboring spins]. It describes entanglement of
the block with the rest of the ground state.
G. Vidal, J.I. Latorre, E. Rico, and A. Kitaev showed that for large blocks
the entropy scales logarithmically. We prove the logarithmic formula for the
leading term and calculate the next term.
We discovered that the dependence on the magnetic field interacting with
spins is very simple: the magnetic field effectively reduce the size of the
subsystem.
We also calculate entropy of a subsystem of a small size. We also evaluated
Renyi and Tsallis entropies of the subsystem. We represented the entropy in
terms of a Toeplitz determinant and calculated the asymptotic analytically.Comment: LATEX, 17 pages, 1 fi
Optical properties of in the normal state
We present the optical reflectance and conductivity spectra for non-oxide
antiperovskite superconductor at different temperatures. The
reflectance drops gradually over a large energy scale up to 33,000 cm,
with the presence of several wiggles. The reflectance has slight temperature
dependence at low frequency but becomes temperature independent at high
frequency. The optical conductivity shows a Drude response at low frequencies
and four broad absorption features in the frequency range from 600 to
33,000 . We illustrate that those features can be well understood from
the intra- and interband transitions between different components of Ni 3d
bands which are hybridized with C 2p bands. There is a good agreement between
our experimental data and the first-principle band structure calculations.Comment: 4 pages, to be published in Phys. Rev.
First-principles calculations of a high-pressure synthesized compound PtC
First-principles density-functional method is used to study the recently
high-pressure synthesized compound PtC. It is confirmed by our calculations
that the platinum carbide has a zinc-blende ground-state phase at zero pressure
and the rock-salt structure is a high-pressure phase. The theoretical
transition pressure from zinc-blende to rock-salt is determined to be 52GPa.
Furthermore, our calculation shows the possibility that the experimentally
synthesized PtC by Ono et al. under high pressure condition might undergo a
transition from rock-salt structure to zinc-blende after the pressure quench to
ambient condition.Comment: A revised versio
A comparison of subgroup construction workers’ perceptions of a safety program
Subcontractor safety performance has become increasingly important due to the extensive use of subcontracting in construction and the elevated safety risks. Ensuring subcontractor safety has also become a major challenge of general contractors (GC)
Out of plane effect on the superconductivity of Sr2-xBaxCuO3+y with Tc up to 98K
A series of new Sr2-xBaxCuO3+y (0 x 0.6) superconductors were prepared using
high-pressure and high-temperature synthesis. A Rietveld refinement based on
powder x-ray diffraction confirms that the superconductors crystallize in the
K2NiF4-type structure of a space group I4/mmm similar to that of La2CuO4 but
with partially occupied apical oxygen sites. It is found that the
superconducting transition temperature Tc of this Ba substituted Sr2CuO3+y
superconductor with constant carrier doping level, i.e., constant d, is
controlled not only by order/disorder of apical-O atoms but also by Ba content.
Tcmax =98 K is achieved in the material with x=0.6 that reaches the record
value of Tc among the single-layer copper oxide superconductors, and is higher
than Tc=95K of Sr2CuO3+y with optimally ordered apical-O atoms. There is
Sr-site disorder in Sr2-xBaxCuO3+y which might lead to a reduction of Tc. The
result indicates that another effect surpasses the disorder effect that is
related either to the increased in-plane Cu-O bond length or to elongated
apical-O distance due to Ba substitution with larger cation size. The present
experiment demonstrates that the optimization of local geometry out of the Cu-O
plane can dramatically enhance Tc in the cuprate superconductors.Comment: 23 Pages, 1 Table, 5 Figure
- …