315 research outputs found
Temperature Dependent Polarized XANES Spectra for Zn-doped LSCO system
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations [i.e. quasiparticle or collective],
spin-charge separation, stripes [static and dynamics], inhomogeneities,
psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in
these materials must be consistently understood. Zn-doped LSCO single crystal
were grown by TSFZ technique. Temperature dependent Polarized XANES [near edge
local structure] spectra were measured at the BL13-B1 [Photon Factory] in the
Flourescence mode from 10 K to 300 K. Since both stripes and nonmagnetic Zn
impurities substituted for Cu give rise to inhomogeneous charge and spin
distribution it is interesting to understand the interplay of Zn impurities and
stripes. To understand these points we have used Zn-doping and some of the
results obtained are as follows: The spectra show a strong dependence with
respect to the polarization angle, , as is evident at any temperature
by comparing the spectra where the electric field vector is parallel with
ab-plane to the one where it is parallel to the c-axis. By using the XANES
[temperature] difference spectra we have determined T* [experimentally we find,
T* 160-170 K] for this sample. The XANES difference spectra shows
that the changes in XANES features are larger in the ab-plane than the c-axis,
this trend is expected since zinc is doped in the ab-plane at the copper site.
Our study also complements the results in literature namely that zinc doping
does not affect the c-axis transport.Comment: To appear in Physica C [ISS2001 Special Issue], related talk
presented at ISS2001 as PC-16, 10 pages revtex and 7 pages of figures (pdf
XANES study of rare-earth valency in LRu4P12 (L = Ce and Pr)
Valency of Ce and Pr in LRu4P12 (L = Ce and Pr) was studied by L2,3-edge
x-ray absorption near-edge structure (XANES) spectroscopy. The Ce-L3 XANES
spectrum suggests that Ce is mainly trivalent, but the 4f state strongly
hybridizes with ligand orbitals. The band gap of CeRu4P12 seems to be formed by
strong hybridization of 4f electrons. Pr-L2 XANES spectra indicate that Pr
exists in trivalent state over a wide range in temperature, 20 < T < 300 K. We
find that the metal-insulator (MI) transition at TMI = 60 K in PrRu4P12 does
not originate from Pr valence fluctuation.Comment: 4 page
Myositis associated with localized lipodystrophy: an unrecognized condition?
Lipodystrophies represent a heterogeneous group of diseases characterized by altered body fat repartition and often metabolic alterations. Here we illustrate a 20 year old male with myositis in association with localized lipodystrophy. Immunohistochemical stainings revealed a regular pattern of dystrophin, dysferlin, sarcoglycans, and theletonin. Furtermore, there was no evidence of Lamin A/C deficiency. A nearly identical clinical and histological picture has been described in three patients up to now. Although it is difficult to speculate on a causative pathophysiological mechanism at this time, it is possible that this association represents an unrecognized condition
A Parallel SSOR Preconditioner for Lattice QCD
A parallelizable SSOR preconditioning scheme for Krylov subspace iterative
solvers in lattice QCD applications involving Wilson fermions is presented. In
actual Hybrid Monte Carlo and quark propagator calculations it helps to reduce
the number of iterations by a factor of 2 compared to conventional odd-even
preconditioning. This corresponds to a gain in cpu-time of 30\% - 70\% over
odd-even preconditioning.Comment: Talk presented at LATTICE96(algorithms), 3 pages, LaTeX file, 3
epsf-files include
Infrared study of spin crossover Fe-picolylamine complex
Infrared (IR) absorption spectroscopy has been used to probe the evolution of
microscopic vibrational states upon the temperature- and photo-induced spin
crossovers in [Fe(2-picolylamine)3]Cl2EtOH (Fe-pic). To overcome the small
sizes and the strong IR absorption of the crystal samples used, an IR
synchrotron radiation source and an IR microscope have been used. The obtained
IR spectra of Fe-pic show large changes between high-spin and low-spin states
for both the temperature- and the photo- induced spin crossovers. Although the
spectra in the temperature- and photo-induced high-spin states are relatively
similar to each other, they show distinct differences below 750 cm-1. This
demonstrates that the photo-induced high-spin state involves microscopically
different characters from those of the temperature-induced high-spin state. The
results are discussed in terms of local pressure and structural deformations
within the picolylamine ligands, and in terms of their possible relevance to
the development of macroscopic photo-induced phase in Fe-pic.Comment: 6 pages (text) and 6 figures,submitted to J. Phys. Soc. Jp
Hadron Mass Predictions of the Valence Approximation to Lattice QCD
We evaluate the infinite volume, continuum limits of eight hadron mass ratios
predicted by lattice QCD with Wilson quarks in the valence (quenched)
approximation. Each predicted ratio differs from the corresponding observed
value by less than 6\%.Comment: 13 pages of Latex + 2 PostScript files attached, IBM/HET 92-
New superconduting cuprates with no effective doping: T'-(La3+)2-x(RE3+)xCuO4
We report the synthesis of new superconducting cuprates T'-La2-xRExCuO4 (RE =
Sm, Eu, Tb, Lu, and Y) using molecular beam epitaxy. The new superconductors
have no effective dopant, at least nominally. The substitution of isovalent RE
for La was essentially performed to stabilize the T' phase of La2CuO4 instead
of the T phase. The maximum Tconset is ~ 25 K and Tczero is ~ 21 K. The keys to
our discovery are (1) the preparation of high-crystalline-quality La-based T'
films by low-temperature (~ 650C) thin film processes, and (2) more thorough
removal of impurity oxygen at the apical site, which is achieved by the larger
in-plane lattice constant (a0) of T'-La2-xRExCuO4 than other T'-Ln2CuO4 (Ln =
Pr, Nd, Sm, Eu, Gd) with the aid of large surface-to-volume ratio of thin
films.Comment: 10 pages, 5 figures (Proceedings of the 16th international symposium
on superconductivity (ISS 2003), to be published in Physica C
Charge order, dielectric response and local structure of La5/3Sr1/3NiO4 system
Charge ordering, dielectric permittivity and local structure of
La5/3Sr1/3NiO4 system have been explored X-ray charge scattering, complex
dielectric impedance spectroscopy, and extended X-ray absorption fine structure
(EXAFS) measurements, made on the same single crystal sample. The local
structure measured by the temperature dependent polarized Ni K-edge EXAFS shows
significant distortions in the NiO2 planes. These local distortions could be
reasonable cause of high dielectric permittivity of the title system (e=100 at
5K) with the charge ordering in this system being a ferroelectric-like second
order transition.Comment: 12 pages, 5 figure
- …