314 research outputs found
Resonant inelastic x-ray scattering study of holon-antiholon continuum in SrCuO2
We report a resonant inelastic x-ray scattering study of charge excitations
in the quasi-one-dimensional Mott insulator SrCuO2. We observe a continuum of
low-energy excitations, in which a highly dispersive feature with a large
sinusoidal dispersion (~1.1 eV) resides. We have also measured the optical
conductivity, and studied the dynamic response of the extended Hubbard model
with realistic parameters, using a dynamical density-matrix renormalization
group method. In contrast to earlier work, we do not find a long-lived exciton,
but rather these results suggest that the excitation spectrum comprises a
holon-antiholon continuum together with a broad resonance.Comment: Final version to be published in Phys. Rev. Let
Resonant inelastic x-ray scattering in one-dimensional copper oxides
The Cu K-edge resonant inelastic x-ray scattering (RIXS) spectrum in
one-dimensional insulating cuprates is theoretically examined by using the
exact diagonalization technique for the extended one-dimensional
Hubbard model with nearest neighbor Coulomb interaction. We find the
following characteristic features that can be detectable by RIXS experiments:
(i) The spectrum with large momentum transfer indicates the formation of
excitons, i.e., bound states of holon and doublon. (ii) The spectrum with small
momentum transfer depends on the incident photon energy. We propose that the
RIXS provides a unique opportunity to study the upper
Hubbard band in one-dimensional cuprates.Comment: 3 pages with 4 figures, minor changes, to appear in Phys.Rev.
Angular Dependence of the High-Magnetic-Field Phase Diagram of URu2Si2
We present measurements of the magnetoresistivity RHOxx of URu2Si2 single
crystals in high magnetic fields up to 60 T and at temperatures from 1.4 K to
40 K. Different orientations of the magnetic field have been investigated
permitting to follow the dependence on Q of all magnetic phase transitions and
crossovers, where Q is the angle between the magnetic field and the easy-axis
c. We find out that all magnetic transitions and crossovers follow a simple
1/cos(Q) -law, indicating that they are controlled by the projection of the
field on the c-axis
Momentum-Resolved Charge Excitations in a Prototype One Dimensional Mott Insulator
We report momentum resolved charge excitations in a one dimensional (1-D)
Mott insulator studied using high resolution (~ 325 meV) inelastic x-ray
scattering over the entire Brillouin zone for the first time. Excitations at
the insulating gap edge are found to be highly dispersive (momentum
dependent)compared to excitations observed in two dimensional Mott insulators.
The observed dispersion in 1-D is consistent with charge excitations involving
holons which is unique to spin-1/2 quantum chain systems. These results point
to the potential utility of inelastic x-ray scattering in providing valuable
information about electronic structure of strongly correlated insulators.Comment: 3 pages, 2 figures, Revised with minor change
Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-Tc superconductors
Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to
highlight an anomalously large band renormalization at high binding energies in
cuprate superconductors: the high energy 'waterfall' or high energy anomaly
(HEA). This paper demonstrates, using a combination of new ARPES measurements
and quantum Monte Carlo simulations, that the HEA is not simply the by-product
of matrix element effects, but rather represents a cross-over from a
quasiparticle band at low binding energies near the Fermi level to valence
bands at higher binding energy, assumed to be of strong oxygen character, in
both hole- and electron-doped cuprates. While photoemission matrix elements
clearly play a role in changing the aesthetic appearance of the band
dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate
description for the physics that underlies the strong band renormalization
giving rise to the HEA. Model calculations of the single-band Hubbard
Hamiltonian showcase the role played by correlations in the formation of the
HEA and uncover significant differences in the HEA energy scale for hole- and
electron-doped cuprates. In addition, this approach properly captures the
transfer of spectral weight accompanying both hole and electron doping in a
correlated material and provides a unifying description of the HEA across both
sides of the cuprate phase diagram.Comment: Original: 4 pages, 4 figures; Replaced: changed and updated content,
12 pages, 6 figure
Charge-density wave formation in Sr_{14}Cu_{24}O_{41}
The electrodynamic response of the spin-ladder compound
SrCaCuO () has been studied from
radiofrequencies up to the infrared. At temperatures below 250 K a pronounced
absorption peak appears around 12 cm in SrCuO for
the radiation polarized along the chains/ladders ().
In addition a strongly temperature dependent dielectric relaxation is observed
in the kHz - MHz range. We explain this behavior by a charge density wave which
develops in the ladders sub-system and produces a mode pinned at 12 cm.
With increasing Ca doping the mode shifts up in frequency and eventually
disappears for because the dimensionality of the system crosses over from
one to two dimensions, giving way to the superconducting ground state under
pressure.Comment: One name added to author list 4 pages, 2 figures, email:
[email protected]
Itinerancy and Hidden Order in
We argue that key characteristics of the enigmatic transition at in indicate that the hidden order is a density wave formed within
a band of composite quasiparticles, whose detailed structure is determined by
local physics. We expand on our proposal (with J.A. Mydosh) of the hidden order
as incommnesurate orbital antiferromagnetism and present experimental
predictions to test our ideas. We then turn towards a microscopic description
of orbital antiferromagnetism, exploring possible particle-hole pairings within
the context of a simple one-band model. We end with a discussion of recent
high-field and thermal transport experiment, and discuss their implications for
the nature of the hidden order.Comment: 18 pages, 7 figures. v2 contains added referenc
ATF3 Plays a Key Role in Kdo2-Lipid A-Induced TLR4-Dependent Gene Expression via NF-κB Activation
Background: Activating transcription factor 3 (ATF3) is a negative regulator of proinflammatory cytokine expression in macrophages, and ATF3 deficient mice are more susceptible to endotoxic shock. This study addresses the role of ATF3 in the Kdo 2-Lipid A-induced Toll-like receptor 4 (TLR4) signaling pathway in mouse embryonic fibroblasts (MEF). Kdo 2-Lipid A upregulates ATF3 expression in wild type MEF cells and induces both nuclear factor kappa B (NF-kB) and c-Jun N-terminal kinase (JNK) activation via the TLR4 signaling pathway, while neither of these pathways is activated in ATF3-/- MEF cells. Interestingly, in contrast to Kdo 2-Lipid A, the activation of both NF-kB and JNK by TNF-a was normal in ATF3-/- MEF cells. Methodology/Principal Findings: We found that several genes were dramatically upregulated in ATF3+/+ MEF cells in response to Kdo2-Lipid A treatment, while little difference was observed in the ATF3-/- MEF cells. However, we also found that the signal intensities of IkBf in ATF3-/- MEF cells were substantially higher than those in wild type MEF cells upon microarray analyses, and upregulated IkBf expression was detected in the cytosol fraction. Conclusions/Significance: Our findings indicate that ATF3 deficiency affects Kdo 2-Lipid A-induced TLR4 signaling pathways in MEF cells, that it may upregulate IkBf expression and that the high levels of IkBf expression in ATF3-/- cells disrupts Kdo2-Lipid A-mediated signaling pathways
Electronic structure of the trilayer cuprate superconductor BiSrCaCuO
The low-energy electronic structure of the trilayer cuprate superconductor
BiSrCaCuO near optimal doping is investigated by
angle-resolved photoemission spectroscopy. The normal state quasiparticle
dispersion and Fermi surface, and the superconducting d-wave gap and coherence
peak are observed and compared with those of single and bilayer systems. We
find that both the superconducting gap magnitude and the relative
coherence-peak intensity scale linearly with for various optimally doped
materials. This suggests that the higher of the trilayer system should be
attributed to parameters that simultaneously enhance phase stiffness and
pairing strength.Comment: 5 pages, 5 figre
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