292 research outputs found
Can antiferromagnetism and superconductivity coexist in the high-field paramagnetic superconductor Nd(O,F)FeAs?
We present measurements of the temperature and field dependencies of the
magnetization M(T,H) of Nd(O0.89F0.11)FeAs at fields up to 33T, which show that
superconductivity with the critical temperature Tc ~ 51K cannot coexist with
antiferromagnetic ordering. Although M(T,H) at 55 < T < 140K exhibits a clear
Curie-Weiss temperature dependence corresponding to the Neel temperature TN ~
11-12K, the behavior of M(T,H) below Tc is only consistent with either
paramagnetism of weakly interacting magnetic moments or a spin glass state. We
suggest that the anomalous magnetic behavior of an unusual high-field
paramagnetic superconductor Nd(O1-xFx)FeAs is mostly determined by the magnetic
Nd ions.Comment: 4 pages, 4 figure
The effect of different baryons impurities
We demonstrate the different effect of different baryons impurities on the
static properties of nuclei within the framework of the relativistic mean-field
model. Systematic calculations show that and has the
same attracting role as hyperon does in lighter hypernuclei.
and hyperon has the attracting role only for the protons
distribution, and has a repulsive role for the neutrons distribution. On the
contrary, and hyperon attracts surrounding neutrons and
reveals a repulsive force to the protons. We find that the different effect of
different baryons impurities on the nuclear core is due to the different third
component of their isospin.Comment: 9 page
Experimental Free-Space Distribution of Entangled Photon Pairs over a Noisy Ground Atmosphere of 13km
We report free-space distribution of entangled photon pairs over a noisy
ground atmosphere of 13km. It is shown that the desired entanglement can still
survive after the two entangled photons have passed through the noisy ground
atmosphere. This is confirmed by observing a space-like separated violation of
Bell inequality of . On this basis, we exploit the distributed
entangled photon source to demonstrate the BB84 quantum cryptography scheme.
The distribution distance of entangled photon pairs achieved in the experiment
is for the first time well beyond the effective thickness of the aerosphere,
hence presenting a significant step towards satellite-based global quantum
communication.Comment: 4 pages, 3 figure
The Yang-Lee zeros of the 1D Blume-Capel model on connected and non-connected rings
We carry out a numerical and analytic analysis of the Yang-Lee zeros of the
1D Blume-Capel model with periodic boundary conditions and its generalization
on Feynman diagrams for which we include sums over all connected and
non-connected rings for a given number of spins. In both cases, for a specific
range of the parameters, the zeros originally on the unit circle are shown to
departure from it as we increase the temperature beyond some limit. The curve
of zeros can bifurcate and become two disjoint arcs as in the 2D case. We also
show that in the thermodynamic limit the zeros of both Blume-Capel models on
the static (connected ring) and on the dynamical (Feynman diagrams) lattice
tend to overlap. In the special case of the 1D Ising model on Feynman diagrams
we can prove for arbitrary number of spins that the Yang-Lee zeros must be on
the unit circle. The proof is based on a property of the zeros of Legendre
Polynomials.Comment: 19 pages, 5 figure
Common Features in Electronic Structure of the Fe-Based Layered Superconductors from Photoemission Spectroscopy
High resolution photoemission measurements have been carried out on
non-superconducting LaOFeAs parent compound and various superconducting
R(O1-xFx)FeAs (R=La, Ce and Pr) compounds. We found that the parent LaOFeAs
compound shows a metallic character. Through extensive measurements, we have
identified several common features in the electronic structure of these
Fe-based compounds: (1). 0.2 eV feature in the valence band; (2). A universal
13~16 meV feature; (3). A clear Fermi cutoff showing zero leading-edge shift in
the superconducting state;(4). Lack of superconducting coherence peak(s); (5).
Near EF spectral weight suppression with decreasing temperature. These
universal features can provide important information about band structure,
superconducting gap and pseudogap in these Fe-based materials.Comment: 5 pages,4 figure
Superconductivity in SmFe1-xMxAsO (M = Co, Rh, Ir)
In this paper we report the comparative study of superconductivity by 3d
(Co), 4d (Rh), 5d (Ir) element doping in SmFeAsO. X-ray diffraction patterns
indicate that the material has formed the ZrCuSiAs-type structure with a space
group P4/nmm. It is found that the antiferromagnetic spin-density-wave (SDW)
order in the parent compounds is rapidly suppressed by Co, Rh, and Ir doping,
and superconductivity emerges. Both electrical resistance and magnetization
measurements show superconductivity up to around 10 K in SmFe1-xMxAsO (M = Co,
Rh, Ir). Co, Rh and Ir locate in the same column in the periodic table of
elements but have different electronic band structure, so comparative study
would add more ingredients to the underlying physics of the iron-based
superconductors.Comment: 16 pages, 4 figures, 1 tabl
Pairing symmetry and properties of iron-based high temperature superconductors
Pairing symmetry is important to indentify the pairing mechanism. The
analysis becomes particularly timely and important for the newly discovered
iron-based multi-orbital superconductors. From group theory point of view we
classified all pairing matrices (in the orbital space) that carry irreducible
representations of the system. The quasiparticle gap falls into three
categories: full, nodal and gapless. The nodal-gap states show conventional
Volovik effect even for on-site pairing. The gapless states are odd in orbital
space, have a negative superfluid density and are therefore unstable. In
connection to experiments we proposed possible pairing states and implications
for the pairing mechanism.Comment: 4 pages, 1 table, 2 figures, polished versio
The effect of internal pressure on the tetragonal to monoclinic structural phase transition in ReOFeAs: the case of NdOFeAs
We report the temperature dependent x-ray powder diffraction of the
quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 K
and 95 K. We have detected the structural phase transition from the tetragonal
phase, with P4/nmm space group, to the orthorhombic or monoclinic phase, with
Cmma or P112/a1 (or P2/c) space group, over a broad temperature range from 150
K to 120 K, centered at T0 ~137 K. Therefore the temperature of this structural
phase transition is strongly reduced, by about ~30K, by increasing the internal
chemical pressure going from LaOFeAs to NdOFeAs. In contrast the
superconducting critical temperature increases from 27 K to 51 K going from
LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped
orthorhombic Cmma phase competes with the superconducting tetragonal phase.
Therefore by controlling the internal chemical pressure in new materials it
should be possible to push toward zero the critical temperature T0 of the
structural phase transition, giving the striped phase, in order to get
superconductors with higher Tc.Comment: 9 pages, 3 figure
Differentiation and Recruitment of Th9 Cells Stimulated by Pleural Mesothelial Cells in Human Mycobacterium tuberculosis Infection
Newly discovered IL-9–producing CD4+ helper T cells (Th9 cells) have been reported to contribute to tissue inflammation and immune responses, however, differentiation and immune regulation of Th9 cells in tuberculosis remain unknown. In the present study, our data showed that increased Th9 cells with the phenotype of effector memory cells were found to be in tuberculous pleural effusion as compared with blood. TGF-β was essential for Th9 cell differentiation from naïve CD4+ T cells stimulated with PMA and ionomycin in vitro for 5 h, and addition of IL-1β, IL-4 or IL-6 further augmented Th9 cell differentiation. Tuberculous pleural effusion and supernatants of cultured pleural mesothelial cells were chemotactic for Th9 cells, and this activity was partly blocked by anti-CCL20 antibody. IL-9 promoted the pleural mesothelial cell repairing and inhibited IFN-γ-induced pleural mesothelial cell apoptosis. Moreover, pleural mesothelial cells promoted Th9 cell differentiation by presenting antigen. Collectively, these data provide new information concerning Th9 cells, in particular the collaborative immune regulation between Th9 cells and pleural mesothelial cells in human M. tuberculosis infection. In particular, pleural mesothelial cells were able to function as antigen-presenting cells to stimulate Th9 cell differentiation
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