10,415 research outputs found
Immunosuppressive Cytokine Gene Polymorphisms And Outcomes After Related And Unrelated Hematopoietic Cell Transplantation
Pressure Effect on the superconducting properties of LaO_{1-x}F_{x}FeAs(x=0.11) superconductor
Diamagnetic susceptibility measurements under high hydrostatic pressure (up
to 1.03 GPa) were carried out on the newly discovered Fe-based superconductor
LaO_{1-x}F_{x}FeAs(x=0.11). The transition temperature T_c, defined as the
point at the maximum slope of superconducting transition, was enhanced almost
linearly by hydrostatic pressure, yielding a dT_c/dP of about 1.2 K/GPa.
Differential diamagnetic susceptibility curves indicate that the underlying
superconducting state is complicated. It is suggested that pressure plays an
important role on pushing low T_c superconducting phase toward the main
(optimal) superconducting phase.Comment: 7 pages, 4 figure
Superconductivity induced by Ni doping in BaFeAs
A series of 122 phase BaFeNiAs ( = 0, 0.055, 0.096, 0.18,
0.23) single crystals were grown by self flux method and a dome-like Ni doping
dependence of superconducting transition temperature is discovered. The
transition temperature reaches a maximum of 20.5 K at = 0.096,
and it drops to below 4 K as 0.23. The negative thermopower in the
normal state indicates that electron-like charge carrier indeed dominates in
this system. This Ni-doped system provides another example of superconductivity
induced by electron doping in the 122 phase.Comment: 7 pages, 5 figures, revised version, added EDX result, accepted for
special issue of NJ
Nernst effect of the new iron-based superconductor LaOFFeAs
We report the first Nernst effect measurement on the new iron-based
superconductor LaOFFeAs . In the normal state, the
Nernst signal is negative and very small. Below a large positive peak
caused by vortex motion is observed. The flux flowing regime is quite large
compared to conventional type-II superconductors. However, a clear deviation of
the Nernst signal from normal state background and an anomalous depression of
off-diagonal thermoelectric current in the normal state between and 50
K are observed. We propose that this anomaly in the normal state Nernst effect
could correlate with the SDW fluctuations.Comment: 8 pages, 4 figures; Latex file changed, references adde
Growth and characterization of A_{1-x}K_xFe_2As_2 (A = Ba, Sr) single crystals with x=0 - 0.4
Single crystals of AKFeAs (A=Ba, Sr) with high quality
have been grown successfully by FeAs self-flux method. The samples have sizes
up to 4 mm with flat and shiny surfaces. The X-ray diffraction patterns suggest
that they have high crystalline quality and c-axis orientation. The
non-superconducting crystals show a spin-density-wave (SDW) instability at
about 173 K and 135 K for Sr-based and Ba-based compound, respectively. After
doping K as the hole dopant into the BaFeAs system, the SDW transition
is smeared, and superconducting samples with the compound of
BaKFeAs (0 0.4) are obtained. The
superconductors characterized by AC susceptibility and resistivity measurements
exhibit very sharp superconducting transition at about 36 K, 32 K, 27 K and 23
K for x= 0.40,0.28,0.25 and 0.23, respectively.Comment: 9 pages, 6 figures, 1 table. This paper together with new data are
modified into a new pape
Pressure effects on the electron-doped high Tc superconductor BaFe(2-x)Co(x)As(2)
Application of pressures or electron-doping through Co substitution into Fe
sites transforms the itinerant antiferromagnet BaFe(2)As(2) into a
superconductor with the Tc exceeding 20K. We carried out systematic transport
measurements of BaFe(2-x)Co(x)As(2) superconductors in pressures up to 2.5GPa,
and elucidate the interplay between the effects of electron-doping and
pressures. For the underdoped sample with nominal composition x = 0.08,
application of pressure strongly suppresses a magnetic instability while
enhancing Tc by nearly a factor of two from 11K to 21K. In contrast, the
optimally doped x=0.20 sample shows very little enhancement of Tc=22K under
applied pressure. Our results strongly suggest that the proximity to a magnetic
instability is the key to the mechanism of superconductivity in iron-pnictides.Comment: 5 figure
Angular dependence of resistivity in the superconducting state of NdFeAsOF single crystals
We report the results of angle dependent resistivity of
NdFeAsOF single crystals in the superconducting state. By
doing the scaling of resistivity within the frame of the anisotropic
Ginzburg-Landau theory, it is found that the angle dependent resistivity
measured under different magnetic fields at a certain temperature can be
collapsed onto one curve. As a scaling parameter, the anisotropy can
be determined for different temperatures. It is found that
increases slowly with decreasing temperature, varying from 5.48
at T=50 K to 6.24 at T=44 K. This temperature dependence can be
understood within the picture of multi-band superconductivity.Comment: 7 pages, 4 figure
Crystallographic Phase Transition and High-Tc Superconductivity in LaFeAsO:F
Undoped LaFeAsO, parent compound of the newly found high-Tc superconductor,
exhibits a sharp decrease in the temperature-dependent resistivity at ~160 K.
The anomaly can be suppressed by F doping and the superconductivity appears
correspondingly, suggesting a close associate of the anomaly with the
superconductivity. We examined the crystal structures, magnetic properties and
superconductivity of undoped (normal conductor) and 14 at.% F-doped LaFeAsO (Tc
= 20 K) by synchrotron X-ray diffraction, DC magnetic measurements, and ab
initio calculations to demonstrate that the anomaly is associated with a phase
transition from tetragonal (P4/nmm) to orthorhombic (Cmma) phases at ~160 K as
well as an antiferromagnetic transition at ~140 K. These transitions can be
explained by spin configuration-dependent potential energy surfaces derived
from the ab initio calculations. The suppression of the transitions is ascribed
to interrelated effects of geometric and electronic structural changes due to
doping by F- ions.Comment: 22 pages, 8 figures, 2 tables, Supplementary information is included
at the end of the document, accepted for publication in Supercond. Sci.
Techno
Identification and shell model calculation of high spin states in 137,138Cs nuclei
High spin states of have been studied by measuring \ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma} coincidences from the spontaneous fission of with the LBNL Gammasphere detector array. The high spin level scheme of the neutron-rich Cs () isotope, , built on the {6}^{\ensuremath{-}} isomeric state, has been established for the first time up to a 4626 keV level, assigned (). The level scheme of has been expanded up to a 5495 keV level, assigned (31/{2}^{\ensuremath{-}}). Spins, parities, and configurations are assigned based on the agreement between experimental level energies and shell model calculations and level systematics. Similarities are observed in the isotones, and , up to as well as in the isotones, and , up to {12}^{\ensuremath{-}}. The shell model calculations indicate the important role played by interactions between the excitation of the valence protons outside the major shell and the valence neutron outside the major shell
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