1,854 research outputs found
Dynamical structure factors of two-leg spin ladder systems
We investigate dynamical properties of two-leg spin ladder systems.
In a strong coupling region, an isolated mode appears in the lowest excited
states, while in a weak coupling region, an isolated mode is reduced and the
lowest excited states become a lower bound of the excitation continuum. We find
in the system with equal intrachain and interchain couplings that due to a
cyclic four-spin interaction, the distribution of the weights for the dynamical
structure factor and characteristics of the lowest excited states are strongly
influenced. The dynamical properties of two systems proposed for are also discussed.Comment: 5 pages, 6 figure
Pressure-induced Superconductivity in a Ferromagnet UGe -- Resistivity Measurements in Magnetic Field --
The electrical resistivity measurements in the magnetic field are carried out
on the pressure-induced superconductor UGe. The superconductivity is
observed from 1.06 to 1.44 GPa. The upper critical field of is
anisotropic where exhibits positive curvature for and
-axis. The characteristic enhancement of is reconfirmed for
-axis. In the temperature and field dependence of resistivity at where the ferromagnetic ordering disappears, it is observed that the
application of the external field along the {\it a}-axis increases the
coefficient of Fermi liquid behavior correspondingly to the
metamagnetic transition.Comment: To be published in the proceeding of the International Conference on
High Pressure Science and Technology(AIRAPT-18),Beijing,China,23-27 July 200
Magnetic Properties of a Pressure-induced Superconductor UGe
We performed the DC-magnetization and neutron scattering experiments under
pressure {\it P} for a pressure-induced superconductor UGe. We found that
the magnetic moment is enhanced at a characteristic temperature {\it T}
in the ferromagnetic state, where {\it T} is smaller than a Curie
temperature {\it T}. This enhancement becomes remarkable in the
vicinity of {\it P} = 1.20 GPa, where {\it T} becomes 0 K
and the superconducting transition temperature {\it T} shows a
maximum. The characteristic temperature {\it T}, which decreases with
increasing pressure, also depends on the magnetic field.Comment: To be published in J.Phys.Soc.Jp
Unusual behaviours and Impurity Effects in the Noncentrosymmetric Superconductor CePt3Si
We report a study in which the effect of defects/impurities, growth process,
off-stoichiometry, and presence of impurity phases on the superconducting
properties of noncentrosymmetric CePt3Si is analysed by means of the
temperature dependence of the magnetic penetration depth. We found that the
linear low-temperature response of the penetration depth -indicative of line
nodes in this material- is robust regarding sample quality, in contrast to what
is observed in unconventional centrosymmetric superconductors with line nodes.
We discuss evidence that the broadness of the superconducting transition may be
intrinsic, though not implying the existence of a second superconducting
transition. The superconducting transition temperature systematically occurs
around 0.75 K in our measurements, in agreement with resistivity and ac
magnetic susceptibility data but in conflict with specific heat, thermal
conductivity and NMR data in which Tc is about 0.5 K. Random defects do not
change the linear low-temperature dependence of the penetration depth in the
heavy-fermion CePt3Si with line nodes, as they do in unconventional
centrosymmetric superconductors with line nodes.Comment: To appear in New Journal of Physic
Optical absorption spectra in SrCu_2O_3 two-leg spin ladder
We calculate the phonon-assisted optical-absorption spectra in SrCu_2O_3
two-leg spin-ladder systems. The results for two models proposed for SrCu_2O_3
are compared. In the model including the effects of a cyclic four-spin
interaction, the shoulder structure appears at 978 cm^{-1} and the peak appears
at 1975 cm^{-1} in the spectrum for polarization of the electric field parallel
to the legs. In the other model which describes a pure two-leg ladder, the peak
appears around the lower edge of the spectrum at 1344 cm^{-1}. The feature can
be effective in determining the proper model for SrCu_2O_3.Comment: 5 pages, 5 figures, to appear in PRB vol. 67 (2003
Spin Fluctuation Induced Superconductivity Controlled by Orbital Fluctuation
A microscopic Hamiltonian reflecting the correct symmetry of -orbitals is
proposed to discuss superconductivity in heavy fermion systems. In the
orbitally degenerate region in which not only spin fluctuations but also
orbital fluctuations develop considerably, cancellation between spin and
orbital fluctuations destabilizes -wave superconductivity.
Entering the non-degenerate region by increasing the crystalline electric
field, -wave superconductivity mediated by antiferromagnetic
spin fluctuations emerges out of the suppression of orbital fluctuations. We
argue that the present scenario can be applied to recently discovered
superconductors CeTIn (T=Ir, Rh, and Co).Comment: 4 pages, 3 figure
Vaccinia virus protein A46R targets multiple Toll-like-interleukin-1 receptor adaptors and contributes to virulence
Viral immune evasion strategies target key aspects of the host antiviral response. Recently, it has been recognized that Toll-like receptors (TLRs) have a role in innate defense against viruses. Here, we define the function of the vaccinia virus (VV) protein A46R and show it inhibits intracellular signalling by a range of TLRs. TLR signalling is triggered by homotypic interactions between the Toll-like-interleukin-1 resistance (TIR) domains of the receptors and adaptor molecules. A46R contains a TIR domain and is the only viral TIR domain-containing protein identified to date. We demonstrate that A46R targets the host TIR adaptors myeloid differentiation factor 88 (MyD88), MyD88 adaptor-like, TIR domain-containing adaptor inducing IFN-beta (TRIF), and the TRIF-related adaptor molecule and thereby interferes with downstream activation of mitogen-activated protein kinases and nuclear factor kappaB. TRIF mediates activation of interferon (IFN) regulatory factor 3 (IRF3) and induction of IFN-beta by TLR3 and TLR4 and suppresses VV replication in macrophages. Here, A46R disrupted TRIF-induced IRF3 activation and induction of the TRIF-dependent gene regulated on activation, normal T cell expressed and secreted. Furthermore, we show that A46R is functionally distinct from another described VV TLR inhibitor, A52R. Importantly, VV lacking the A46R gene was attenuated in a murine intranasal model, demonstrating the importance of A46R for VV virulence
Thermal transport in the hidden-order state of URuSi
We present a study of thermal conductivity in the normal state of the
heavy-fermion superconductor URuSi. Ordering at 18K leads to a
steep increase in thermal conductivity and (in contrast with all other cases of
magnetic ordering in heavy-fermion compounds) to an enhancement of the Lorenz
number. By linking this observation to several other previously reported
features, we conclude that most of the carriers disappear in the ordered state
and this leads to a drastic increase in both phononic and electronic
mean-free-path.Comment: 5 pages including 4 figure
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