2,709 research outputs found
Carbon-substitution effect on the electronic properties of MgB single crystals
The electronic properties of the carbon substituted MgB single crystals
are reported. The carbon substitution drops T below 2 K. In-plane
resistivity shows a remarkable increase in residual resistivity by
C-substitution, while the change of in-plane/out-of-plane Hall coefficients is
rather small. Raman scattering spectra indicate that the E-phonon
frequency radically hardens with increasing the carbon-content, suggesting the
weakening of electron-phonon coupling. Another striking C-effect is the
increases of the second critical fields in both in-plane and out-of-plane
directions, accompanied by a reduction in the anisotropy ratio. The possible
changes in the electronic state and the origin of T-suppression by
C-substitution are discussed.Comment: 6 pages, 8 figure
Molecular and Genetic Determinants of Glioma Cell Invasion.
A diffusely invasive nature is a major obstacle in treating a malignant brain tumor, "diffuse glioma", which prevents neurooncologists from surgically removing the tumor cells even in combination with chemotherapy and radiation. Recently updated classification of diffuse gliomas based on distinct genetic and epigenetic features has culminated in a multilayered diagnostic approach to combine histologic phenotypes and molecular genotypes in an integrated diagnosis. However, it is still a work in progress to decipher how the genetic aberrations contribute to the aggressive nature of gliomas including their highly invasive capacity. Here we depict a set of recent discoveries involving molecular genetic determinants of the infiltrating nature of glioma cells, especially focusing on genetic mutations in receptor tyrosine kinase pathways and metabolic reprogramming downstream of common cancer mutations. The specific biology of glioma cell invasion provides an opportunity to explore the genotype-phenotype correlation in cancer and develop novel glioma-specific therapeutic strategies for this devastating disease
Superconducting gap of overdoped Tl2Ba2CuO6+d observed by Raman scattering
We report Raman scattering spectra for single crystals of overdoped
Tl2Ba2CuO6+d (Tl-2201) at low temperatures. It was observed that the
pair-breaking peaks in A1g and B1g spectra radically shift to lower energy with
carrier doping. We interpret it as s-wave component mixing into d-wave,
although the crystal structure is tetragonal. Since similar phenomena were
observed also in YBa2Cu3Oy and Bi2Sr2CaCu2Oz, we conclude that s-wave mixing is
a common property for overdoped high-Tc superconductors.Comment: 8 pages, 3 figures, proceedings of SNS200
Origin of superconductivity transition broadening in MgB2
We report resistivity and magnetization of single crystal MgB2, focusing on
the broadening of superconducting (SC) transition in magnetic fields. In-plane
and out-of-plane resistivity indicate that the broadening of superconducting
transition is independent of Lorentz force and that it is merely dependent on
the magnetic field direction. In magnetization, diamagnetic signal begins to
appear at almost the same temperature as the onset temperature of resistivity
transition. These results suggest that the broadening is attributed not to the
surface superconductivity but to the superconducting fluctuation or the
vortex-liquid picture, owing to the short coherence length and the high
transition temperature of MgB2.Comment: 8pages, 6 figures, to be published in Physica
Oxygen Phonon Branches in Detwinned YBa2Cu3O7
We report results of inelastic neutron scattering measurements of phonon
dispersions on a detwinned sample of YBaCu3O7 and compare them with model
calculations. Plane oxygen bond stretching phonon branches disperse steeply
downwards from the zone center in both the a and the b direction indicating a
strong electron-phonon coupling. Half way to the zone boundary, the phonon
peaks become ill-defined but we see no need to invoke unit cell doubling or
charge stripe formation: lattice dynamical shell model calculations predict
such behavior as a result of branch anticrossings. There were no observable
superconductivity-related temperature effects on selected plane oxygen bond
stretching modes measured on a twinned sample.Comment: 5 pages, 3 figures, To appear in Journal of Low Temperature Physics
(Proceedings of MOS2002; Revised version (1) with many changes throughout the
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