665 research outputs found
Exciton Mediated Triplet Superconductivity in Th System PrOs4Sb12
In PrOs4Sb12, the lowest-lying singlet and triplet states in a Pr 4f^2
configuration hybridize with conduction electrons having local a_u and t_u
point-group symmetries. It is shown that for an attractive triplet pairing
interaction, the orbital degrees of freedom of the t_u component are important.
In addition, the Th point-group symmetry characteristic of skutterudites plays
an important role in stabilizing triplet superconductivity.Comment: 4 pages, 2 figure
Effects of Impurities with Singlet-Triplet Configuration on Multiband Superconductors
Roles of multipole degrees of freedom in multiband superconductors are
investigated in a case of impurities whose low-lying states consist of singlet
ground and triplet excited states, which is related to the experimental fact
that the transition temperature is increased by Pr substitution for
La in LaOsSb. The most important contribution to the
increase comes from the inelastic interband scattering of electrons coupled to
quadrupole or octupole moments of impurities. It is found that a magnetic field
modifies an effective pairing interaction and the scattering anisotropy appears
in the field-orientation dependence of the upper critical field
in the vicinity of , although a uniaxial anisotropic field is
required for experimental detection. This would be proof that the Pr internal
degrees of freedom are relevant to the stability of superconductivity in
(LaPr)OsSb.Comment: 10 pages, 5 figures, to appear in J. Phys. Soc. Jp
ZEB1 limits adenoviral infectability by transcriptionally repressing the Coxsackie virus and Adenovirus Receptor
<p>Abstract</p> <p>Background</p> <p>We have previously reported that RAS-MEK (Cancer Res. 2003 May 1;63(9):2088-95) and TGF-β (Cancer Res. 2006 Feb 1;66(3):1648-57) signaling negatively regulate coxsackie virus and adenovirus receptor (CAR) cell-surface expression and adenovirus uptake. In the case of TGF-β, down-regulation of CAR occurred in context of epithelial-to-mesenchymal transition (EMT), a process associated with transcriptional repression of E-cadherin by, for instance, the E2 box-binding factors Snail, Slug, SIP1 or ZEB1. While EMT is crucial in embryonic development, it has been proposed to contribute to the formation of invasive and metastatic carcinomas by reducing cell-cell contacts and increasing cell migration.</p> <p>Results</p> <p>Here, we show that ZEB1 represses CAR expression in both PANC-1 (pancreatic) and MDA-MB-231 (breast) human cancer cells. We demonstrate that ZEB1 physically associates with at least one of two closely spaced and conserved E2 boxes within the minimal CAR promoter here defined as genomic region -291 to -1 relative to the translational start ATG. In agreement with ZEB1's established role as a negative regulator of the epithelial phenotype, silencing its expression in MDA-MB-231 cells induced a partial Mesenchymal-to-Epithelial Transition (MET) characterized by increased levels of E-cadherin and CAR, and decreased expression of fibronectin. Conversely, knockdown of ZEB1 in PANC-1 cells antagonized both the TGF-β-induced down-regulation of E-cadherin and CAR and the reduction of adenovirus uptake. Interestingly, even though ZEB1 clearly contributes to the TGF-β-induced mesenchymal phenotype of PANC-1 cells, TGF-β did not seem to affect ZEB1's protein levels or subcellular localization. These findings suggest that TGF-β may inhibit CAR expression by regulating factor(s) that cooperate with ZEB1 to repress the CAR promoter, rather than by regulating ZEB1 expression levels. In addition to the negative E2 box-mediated regulation the minimal CAR promoter is positively regulated through conserved <it>ETS </it>and <it>CRE </it>elements.</p> <p>Conclusions</p> <p>This report provides evidence that inhibition of ZEB1 may improve adenovirus uptake of cancer cells that have undergone EMT and for which ZEB1 is necessary to maintain the mesenchymal phenotype. Targeting of ZEB1 may reverse some aspects of EMT including the down-regulation of CAR.</p
Multipole State of Heavy Lanthanide Filled Skutterudites
We discuss multipole properties of filled skutterudites containing heavy
lanthanide Ln from a microscopic viewpoint on the basis of a seven-orbital
Anderson model. For Ln=Gd, in contrast to naive expectation, quadrupole moments
remain in addition to main dipole ones. For Ln=Ho, we find an exotic state
governed by octupole moment. For Ln=Tb and Tm, no significant multipole moments
appear at low temperatures, while for Ln=Dy, Er, and Yb, dipole and
higher-order multipoles are dominant. We briefly discuss possible relevance of
these multipole states with actual materials.Comment: 5 pages, 3 figure
Orbitally Degenerate Spin-1 Model for Insulating V2O3
Motivated by recent neutron, X-ray absorption and resonant scattering
experiments, we revisit the electronic structure of V2O3. We propose a model in
which S=1 V3+ ions are coupled in the vertical V-V pairs forming two-fold
orbitally degenerate configurations with S=2. Ferro-orbital ordering of the V-V
pairs gives a description which is consistent with all experiments in the
antiferromagnetic insulating phase.Comment: 4 pages, including three figure
Octupolar ordering of Gamma8 ions in magnetic field
We study f-electron lattice models which are capable of supporting octupolar,
as well dipolar and quadrupolar, order. Analyzing the properties of the Gamma8
ground state quartet, we find that (111)-type combinations of the Gamma5
octupoles Tbeta(111)=Tbeta(x)+Tbeta(y)+Tbeta(z) are the best candidates for
octupolar order parameters. Octupolar ordering induces Gamma5-type quadrupoles
as secondary order parameter. Octupolar order is to some extent assisted, but
in its basic nature unchanged, by allowing for the presence of quadrupolar
interactions. In the absence of an external magnetic field, equivalent results
hold antiferro-octupolar ordering on the fcc lattice. In this sense, the choice
of our model is motivated by the recent suggestion of octupolar ordering in
NpO2.
The bulk of our paper is devoted to a study of the effect of an external
magnetic field on ferro-octupolar ordering. We found that octupolar order
survives up to a critical magnetic field if the field is lying in specific
directions, while for general field directions, the underlying symmetry of the
model is destroyed and therefore the phase transition suppressed even in weak
fields. Field-induced multipoles and field-induced couplings between various
order parameters are discussed on the basis of a group theoretical analysis of
the Helmholtz potential. We also studied the effect of octupolar ordering on
the non-linear magnetic susceptibility which satisfies Ehrenfest-type relations
at continuous octupolar transitions.Comment: 29 pages, 10 figures LaTeX In its contents, the present version
agrees with the published one (see Journal Reference below). Essential
additions to the text in Sec. III, otherwise some change of wording, and
minor correction
Charge Kondo effect toward a non-Fermi-liquid fixed point in the orbitally degenerate exchange model
We show that a Kondo-type model with an orbital degeneracy has a new
non-Fermi-liquid fixed point. Near the fixed point the spin degrees of freedom
are completely quenched, and the residual charge degrees of freedom lead to the
multi-channel Kondo effect. Anomalous behavior appears in electric and thermal
properties, but the magnetic susceptibility should show the local Fermi-liquid
behavior. The non-Fermi-liquid fixed point becomes unstable against
perturbations breaking the particle-hole symmetry. We derive these results
using the third-order scaling for a spherically symmetric model with a
fictitious spin. In contrast to the Coqblin-Schrieffer model, the present model
respects different time-reversal properties of multipole operators.Comment: 4 pages, 2 eps figures, to appear in J. Phys. Soc. Jpn. 68 No.
Resonant X-Ray Scattering from the Quadrupolar Ordering Phase of CeB_6
We theoretically investigate the origin of the resonant x-ray scattering
(RXS) signal near the Ce absorption edge in the quadrupolar ordering
phase of CeB, considering the intersite interaction between the
states in the initial state. The anisotropic charge distribution of the
states modulates the states through the intra-atomic Coulomb interaction
and thereby generates a large RXS superlattice intensity. The temperature and
magnetic field dependence indicates that the induced dipolar and octupolar
orders have little influence on the RXS spectra, in good agreement with the
recent experiment.Comment: 4 pages, 4 figure
Kondo Effects and Multipolar Order in the cubic PrTr2Al20 (Tr=Ti, V)
Our single crystal study reveals that PrTr2Al20 (Tr = Ti and V) provides the
first examples of a cubic {\Gamma}3 nonmagnetic ground doublet system that
shows the Kondo effect including a -ln T dependent resistivity. The {\Gamma}3
quadrupolar moments in PrV2Al20 induce anomalous metallic behavior through
hybridization with conduction electrons, such as T^{1/2} dependent resistivity
and susceptibility below ~ 20 K down to its ordering temperature T_O = 0.6 K.
In PrTi2Al20, however, quadrupoles are well-localized and exhibit an order at
T_O = 2.0 K. Stronger Kondo coupling in PrV2Al20 than in PrTi2Al20 suppresses
quadrupolar ordering, and instead promotes hybridization between the {\Gamma}3
doublet and conduction electrons, leading to most likely the quadrupolar Kondo
effect.Comment: 12 pages, 4 figure
Realization of Heavy Local Fermi Liquid and Non-Fermi Liquid in f Crystalline-Electric-Field Singlet-Triplet Configuration
Using the numerical renormalization group method, we investigate an extended
Anderson model, in which correlated electrons with the
(singlet)-(triplet) f crystalline-electric-field (CEF)
configuration hybridize with conduction electrons of (doublet) and
(quartet) under cubic symmetry, from a strong spin-orbit
interaction limit. For the case of the parameters relevant to PrFe4P12, the
system is under competition between the CEF singlet fixed point and the
multichannel
Kondo non-Fermi liquid fixed point arising from the quadrupolar coupling
between the impurity with pseudospin 1 and the conduction electron with
pseudospin 3/2 . We consider that this result reveals the origin of the
heaviness of the effective mass and non-Fermi liquid behavior of the Pr- based
filled skutterudite compounds.Comment: 9 pages, 5 figure
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