221 research outputs found
Local Lattice Instability and Superconductivity in LaSrCuMO (M=Mn, Ni, and Co)
Local lattice structures of LaSrCuMO (M=Mn,
Ni, and Co) single crystals are investigated by polarized extended x-ray
absorption fine structure (EXAFS). The local lattice instability at low
temperature is described by in-plane Cu-O bond splitting. We find that
substitution of Mn for Cu causes little perturbation of local lattice
instability while Ni and Co substitution strongly suppresses the instability.
The suppression of superconductivity by Cu-site substitution is related to the
perturbation of lattice instability, indicating that local lattice instability
(polaron) plays an important role in superconductivity
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
Lattice Instability in High Temperature Superconducting Cuprates and FeAs Systems: Polarons Probed by EXAFS
Carrier-induced lattice distortion (signature of polaron) in oxypnictide superconductors is found by an instantaneous local probe, extended X-ray absorption fine structure (EXAFS). Polaron formation is detected as two distinct nearest neighbor distances (FeAs), implying an incoherent local mode that develops coherence at the critical temperature. Comparing the results with the unusual lattice response in cuprate superconductors, intimate correlation between evolution of local lattice mode and superconductivity is revealed. The results suggest that strong electron-lattice interaction is present as a common ingredient in the microscopic mechanism of superconducting transition. The effect of magnetic impurity atoms in cuprates further indicates that magnetic scattering becomes diluted as long as polaron formation is conserved. We argue that polaron coherence dominates electrical conduction and magnetic interaction in oxypnictide and cuprate superconductors
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
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
SET based experiments for HTSC materials: II
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. In this note we further discuss our original suggestion of using
Single Electron Tunneling Transistor
[SET] based experiments to understand the role of charge dynamics in these
systems. Assuming that SET operates as an efficient charge detection system we
can expect to understand the underlying physics of charge transport and charge
fluctuations in these materials for a range of doping. Experiments such as
these can be classed in a general sense as mesoscopic and nano characterization
of cuprates and related materials. In principle such experiments can show if
electron is fractionalized in cuprates as indicated by ARPES data. In contrast
to flux trapping experiments SET based experiments are more direct in providing
evidence about spin-charge separation. In addition a detailed picture of nano
charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P:
P10-0
High real-space resolution measurement of the local structure of Ga_1-xIn_xAs using x-ray diffraction
High real-space resolution atomic pair distribution functions (PDF)s from the
alloy series Ga_1-xIn_xAs have been obtained using high-energy x-ray
diffraction. The first peak in the PDF is resolved as a doublet due to the
presence of two nearest neighbor bond lengths, Ga-As and In-As, as previously
observed using XAFS. The widths of nearest, and higher, neighbor pairs are
analyzed by separating the strain broadening from the thermal motion. The
strain broadening is five times larger for distant atomic neighbors as compared
to nearest neighbors. The results are in agreement with model calculations.Comment: 4 pages, 5 figure
Lattice QCD Calculation of Hadron Scattering Lengths
Method of calculating hadron multi-point functions and disconnected quark
loop contributions which are not readily accessible through conventional
techniques is proposed. Results are reported for pion-pion, pion-nucleon and
nucleon-nucleon scattering lengths and the flavor singlet-non singlet meson
mass splitting estimated in quenched QCD.Comment: 6 pages. Contribution to Lattice '93. Latex file, style file
espcrc2.sty needed.(appended at the end) Figures are also included as epsf
file
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