2,979 research outputs found
Universal relationship between crystallinity and irreversibility field of MgB2
The relationship between irreversibility field, Hirr, and crystallinity of
MgB2 bulks including carbon substituted samples was studied. The Hirr was found
to increase with an increase of FWHM of MgB2 (110) peak, which corresponds to
distortion of honeycomb boron sheet, and their universal correlation was
discovered even including carbon substituted samples. Excellent Jc
characteristics under high magnetic fields were observed in samples with large
FWHM of (110) due to the enhanced intraband scattering and strengthened grain
boundary flux pinning. The relationship between crystallinity and Hirr can
explain the large variation of Hirr for MgB2 bulks, tapes, single crystals and
thin films.Comment: 3 pages, 4 figures, to be published in Appl. Phys. Lett. (in press
Dimensionality-driven spin-flop transition in quasi-one-dimensional PrBa2Cu4O8
In the quasi-one-dimensional cuprate PrBaCuO, the Pr cations
order antiferromagnetically at 17 K in zero field. Through a combination of
magnetic susceptibility, torque magnetometry, specific heat and interchain
transport measurements, the anisotropic temperature-magnetic field phase
diagram associated with this ordering has been mapped out. A low-temperature
spin-flop transition in the Pr sub-lattice is found to occur at the same
magnetic field strength and orientation as a dimensional crossover in the
ground state of the metallic CuO chains. This coincidence suggests that the
spin reorientation is driven by a change in the anisotropic
Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction induced by a corresponding
change in effective dimensionality of the conduction electrons.Comment: 8 pages, 8 figure
Biaxial magnetic alignment in twinned REBa[2]Cu[3]O[y]superconductors
Biaxial magnetic alignment of REBa[2]Cu[3]O[y] (RE123, RE = Y, Nd, Sm, Dy, and Er) superconductor powders containing twin microstructures was demonstrated. Appropriate choice of RE effectively improved the degrees of in-plane and c-axis orientation in RE123 powder samples aligned under modulated rotating magnetic fields at room temperature. From the relationship between the magnetic field strength and the degrees of orientation, it is concluded that heavy RE ions induced the improvement of the in-plane magnetic anisotropies in RE123 grains with twin microstructures
Possible co-existence of local itinerancy and global localization in a quasi-one-dimensional conductor
In the chain compound PrBaCuO localization appears simultaneously
with a dimensional crossover in the electronic ground state when the scattering
rate in the chains exceeds the hopping rate between the chains. Here we report
the discovery of a large, transverse magnetoresistance in PrBaCuO
in the localized regime. This result suggests a novel form of localization
whereby electrons retain their metallic (quasi-one-dimensional) character over
a microscopic length scale despite the fact that macroscopically, they exhibit
localized (one-dimensional) behavior.Comment: 4 pages, 4 Figure
Spin dynamics and antiferromagnetic order in PrBa2Cu4O8 studied by Cu nuclear respnance
Results of the nuclear resonance experiments for the planar Cu sites in
PrBa2Cu4O8 are presented. The NMR spectrum at 1.5 K in zero magnetic field
revealed an internal field of 6.1 T, providing evidence for an
antiferromagnetic order of the planar Cu spins. This confirms that the CuO2
planes are insulating, therefore, the metallic conduction in this material is
entirely due to the one-dimensional zigzag Cu2O2 chains. The results of the
spin-lattice relaxation rates measured by zero field NQR above 245 K in the
paramagnetic state are explained by the theory for a Heisenberg model on a
square lattice.Comment: 4 pages, 2 figure
Angle-resolved photoemission study of insulating and metallic Cu-O chains in PrBaCuO and PrBaCuO
We compare the angle-resolved photoemission spectra of the hole-doped Cu-O
chains in PrBaCuO (Pr123) and in PrBaCuO (Pr124).
While, in Pr123, a dispersive feature from the chain takes a band maximum at
(momentum along the chain) and loses its spectral weight
around the Fermi level, it reaches the Fermi level at in
Pr124. Although the chains in Pr123 and Pr124 are approximately 1/4-filled,
they show contrasting behaviors: While the chains in Pr123 have an instability
to charge ordering, those in Pr124 avoid it and show an interesting spectral
feature of a metallic coupled-chain system.Comment: 4 pages, 5 figures, to be published in PR
Elevated Expression of MAPK Phosphatase 3 in Breast Tumors—A Mechanism of Tamoxifen Resistance
Antiestrogen resistance is a major clinical problem in the treatment of breast cancer. Altered growth factor signaling with estrogen receptor (ER) α has been shown to be associated with the development of resistance. Gene expression profiling was utilized to identify MAPK phosphatase 3 (MKP3) whose expression was correlated with response to the antiestrogen tamoxifen in both patients and in vitro derived cell line models. Overexpression of MKP3 rendered ERα-positive breast cancer cells resistant to the growth inhibitory effects of tamoxifen, and enhanced tamoxifen agonist activity in endometrial cells. MKP3 overexpression was associated with lower levels of activated ERK1,2 phosphorylation in the presence of estrogen, but that estrogen deprivation and tamoxifen treatment decreased MKP3 phosphatase activity, leading to an up-regulation of pERK1,2 MAPK, phosphoserine 118 of ERα, and cyclin D1. The MEK inhibitor PD98059 blocked tamoxifen-resistant growth. Accumulation of reactive oxygen species was observed with tamoxifen treatment of MKP3 overexpressing cells, and antioxidant treatment increased MKP3 phosphatase activity, thereby blocking resistance. Furthermore, PD98059 increased the levels of phospho-JNK in tamoxifen-treated MKP3 overexpressing cells, suggesting an interaction between MKP3 levels, activation of ERK1,2 MAPK, and JNK signaling in human breast cancer cells. MKP3 represents a novel mechanism of resistance which may be a potential biomarker for the use of ERK1,2 and/or JNK inhibitors in combination with tamoxifen treatment
Possible high temperature superconductivity in Ti-doped A-Sc-Fe-As-O (A= Ca, Sr) system
We report a systematic study on the effect of partial substitution of
Sc by Ti in SrScFeAsO, CaScFeAsO and
SrScFeAsO on their electrical properties. High
level of doping results in an increased carrier concentration and leads to the
appearance of superconductivity with the onset of T up to 45 K.Comment: 8 pages, 4 figures, 2 new figure
Charge Fluctuations in Geometrically Frustrated Charge Ordering System
Effects of geometrical frustration in low-dimensional charge ordering systems
are theoretically studied, mainly focusing on dynamical properties. We treat
extended Hubbard models at quarter-filling, where the frustration arises from
competing charge ordered patterns favored by different intersite Coulomb
interactions, which are effective models for various charge transfer-type
molecular conductors and transition metal oxides. Two different lattice
structures are considered: (a) one-dimensional chain with intersite Coulomb
interaction of nearest neighbor V_1 and that of next-nearest neighbor V_2, and
(b) two-dimensional square lattice with V_1 along the squares and V_2 along one
of the diagonals. From previous studies, charge ordered insulating states are
known to be unstable in the frustrated region, i.e., V_1 \simeq 2V_2 for case
(a) and V_1 \simeq V_2 for case (b), resulting in a robust metallic phase even
when the interaction strenghs are strong. By applying the Lanczos exact
diagonalization to finite-size clusters, we have found that fluctuations of
different charge order patterns exist in the frustration-induced metallic
phase, showing up as characteristic low energy modes in dynamical correlation
functions. Comparison of such features between the two models are discussed,
whose difference will be ascribed to the dimensionality effect. We also point
out incommensurate correlation in the charge sector due to the frustration,
found in one-dimensional clusters.Comment: 8 pages, 9 figure
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