146 research outputs found
Magnetoresistance Anomalies in Antiferromagnetic YBa_2Cu_3O_{6+x}: Fingerprints of Charged Stripes
We report novel features in the in-plane magnetoresistance (MR) of heavily
underdoped YBa_2Cu_3O_{6+x}, which unveil a developed ``charged stripe''
structure in this system. One of the striking features is an anisotropy of the
MR with a "d-wave" symmetry upon rotating the magnetic field H within the ab
plane, which is caused by the rotation of the stripes with the external field.
With decreasing temperature, a hysteresis shows up below ~20 K in the MR curve
as a function of H and finally below 10 K the magnetic-field application
produces a persistent change in the resistivity. This "memory effect" is caused
by the freezing of the directionally-ordered stripes.Comment: 4 pages, 6 figures, final version, to appear in 4 October 1999 issue
of PR
Charge Localization from Local Destruction of Antiferromagnetic Correlation in Zn-doped YBa2Cu3O7-d
The in-plane normal-state resistivity of Zn-doped YBa2Cu3O7-d single crystals
is measured down to low temperatures by suppressing superconductivity with
magnetic fields up to 18 T. Substitution of Cu with Zn in the CuO2 planes is
found to induce carrier localization at low temperatures in "clean" samples
with kF l > 5, where the mean free path l is larger than the electron wave
length and thus localization is not normally expected. The destruction of the
local antiferromagnetic correlation among Cu spins by Zn is discussed to be the
possible origin of this unusual charge localization.Comment: 4 pages of LaTeX (revtex and epsf) including 4 postscript figure
Electrical Resistivity Anisotropy from Self-Organized One-Dimensionality in High-Temperature Superconductors
We investigate the manifestation of the stripes in the in-plane resistivity
anisotropy in untwinned single crystals of La_{2-x}Sr_{x}CuO_{4} (x = 0.02 -
0.04) and YBa_{2}Cu_{3}O_{y} (y = 6.35 - 7.0). It is found that both systems
show strongly temperature-dependent in-plane anisotropy in the lightly
hole-doped region and that the anisotropy in YBa_{2}Cu_{3}O_{y} grows with
decreasing y below about 6.60 despite the decreasing orthorhombicity, which
gives most direct evidence that electrons self-organize into a macroscopically
anisotropic state. The transport is found to be easier along the direction of
the spin stripes already reported, demonstrating that the stripes are
intrinsically conducting in cuprates.Comment: 5 pages, 4 figures (including one color figure), final version
accepted for publication in Phys. Rev. Let
Thermal conductivity of lightly Sr- and Zn-doped LaCuO single crystals
Both ab-plane and c-axis thermal conductivities ( and
) of lightly doped LaSrCuO and
LaCuZnO single crystals ( or = 0 -- 0.04) are
measured from 2 to 300 K. It is found that the low-temperature phonon peak (at
20 -- 25 K) is significantly suppressed upon Sr or Zn doping even at very low
doping, though its precise doping dependences show interesting differences
between the Sr and Zn dopants, or between the plane and the c axis. Most
notably, the phonon peak in decreases much more quickly with Sr
doping than with Zn doping, while the phonon-peak suppression in
shows an opposite trend. It is discussed that the scattering of phonons by
stripes is playing an important role in the damping of the phonon heat
transport in lightly doped LSCO, in which static spin stripes has been observed
by neutron scattering. We also show and data of
LaNdSrCuO and
LaEuSrCuO single crystals to compare with the
data of the lightly doped crystals for the discussion of the role of stripes.
At high temperature, the magnon peak (i.e., the peak caused by the spin heat
transport near the N\'{e}el temperature) in is found to be
rather robust against Zn doping, while it completely disappears with only 1% of
Sr doping.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.
High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A
We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on
the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk
object, with a gap structure separating its inner and outer disks. Our imagery
taken with the 0.15 (21 AU) radius coronagraphic mask has revealed a strongly
polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a
spatial resolution of 0.1 (14 AU). It is inclined by 46 \pm 2 degree as the
west side is nearest. Although SED modeling and sub-millimeter imagery
suggested the presence of a gap in the disk, with the inner edge of the outer
disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at
the limit of our inner working angle (23 AU) at the near-infrared wavelength.
We attribute the observed strong polarization (up to 66 %) to light scattering
by dust grains in the disk. However, neither polarization models of the
circumstellar disk based on Rayleigh scattering nor Mie scattering
approximations were consistent with the observed azimuthal profile of the
polarization degrees of the disk. Instead, a geometric optics model of the disk
with nonspherical grains with the radii of 30 micron meter is consistent with
the observed profile. We suggest that the dust grains have experienced frequent
collisional coagulations and have grown in the circumstellar disk of UX Tau A.Comment: 20 pages, 8 figures, and 1 table. accepted to PAS
Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates
The low-energy excitations of the lightly doped cuprates were studied by
angle-resolved photoemission spectroscopy. A finite gap was measured over the
entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This
effect was observed to be generic to the normal states of numerous cuprates,
including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and
electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to
close with increasing carrier doping. We consider various scenarios to explain
our results, including the possible effects of chemical disorder, electronic
inhomogeneity, and a competing phase.Comment: To appear in Phys. Rev.
Stromal micropapillary pattern predominant lung adenocarcinoma - a report of two cases
Generally, adenocarcinomas with micropapillary pattern, featuring small papillary tufts lacking a central fibrovascular core, are thought to have poor prognosis. This pattern has been described in various organs. However, tumor cells with micropapillary pattern of lung adenocarcinoma are more often seen to float within alveolar spaces (aerogenous micropapillary pattern, AMP) than in fibrotic stroma like other organs (stromal micropapillary pattern, SMP) and SMP predominant lung adenocarcinoma (SMPPLA) has not been well described yet. We presented two cases of SMPPLA which were found in the last four years. Both the cases showed more than 50% of SMP in the tumor area. The majority of the stromal micropapillary clusters expressed MUC1 and epithelial membrane antigen along the outer surface of cell membrane. On the other hand, connective tissues surrounding stromal micropapillary clusters showed no reactivity for epithelial markers (thyroid transcription factor-1 and cytokeratin) or endothelial marker (D2-40 and CD34). It means clusters of SMP do not exist within air space or lymphatic or vessel lumens. The tumors with SMP often presented lymphatic permeation and vessel invasion, and intriguingly, one of the two cases showed metastasis to the mediastinal lymph node. Additionally, both the cases showed EGFR point mutations of exon 21. These results suggest that SMPPLA might be associated with poor prognosis and effective for EGFR tyrosine kinase inhibitors
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