1,880 research outputs found
Universal quasiparticle decoherence in hole- and electron-doped high-Tc cuprates
We use angle-resolved photoemission to unravel the quasiparticle decoherence
process in the high- cuprates. The coherent band is highly renormalized,
and the incoherent part manifests itself as a nearly vertical ``dive'' in the
- intensity plot that approaches the bare band bottom. We find that the
coherence-incoherence crossover energies in the hole- and electron-doped
cuprates are quite different, but scale to their corresponding bare bandwidth.
This rules out antiferromagnetic fluctuations as the main source for
decoherence. We also observe the coherent band bottom at the zone center, whose
intensity is strongly suppressed by the decoherence process. Consequently, the
coherent band dispersion for both hole- and electron-doped cuprates is
obtained, and is qualitatively consistent with the framework of Gutzwiller
projection.Comment: 4 pages, 4 figure
Unusual photoemission resonances of oxygen-dopant induced states in BiSrCaCuO
We have performed an angular-resolved photoemission study of underdoped,
optimally doped and overdoped BiSrCaCuO samples using a
wide photon energy range (15 - 100 eV). We report a small and broad
non-dispersive A peak in the energy distribution curves whose intensity
scales with doping. We attribute it to a local impurity state similar to the
one observed recently by scanning tunneling spectroscopy and identified as the
oxygen dopants. Detailed analysis of the resonance profile and comparison with
the single-layered BiSrCuO suggest a mixing of this local
state with Cu via the apical oxygens.Comment: 4 pages, 4 figure
Coupling of spin and orbital excitations in the iron-based superconductor FeSe(0.5)Te(0.5)
We present a combined analysis of neutron scattering and photoemission
measurements on superconducting FeSe(0.5)Te(0.5). The low-energy magnetic
excitations disperse only in the direction transverse to the characteristic
wave vector (1/2,0,0), whereas the electronic Fermi surface near (1/2,0,0)
appears to consist of four incommensurate pockets. While the spin resonance
occurs at an incommensurate wave vector compatible with nesting, neither
spin-wave nor Fermi-surface-nesting models can describe the magnetic
dispersion. We propose that a coupling of spin and orbital correlations is key
to explaining this behavior. If correct, it follows that these nematic
fluctuations are involved in the resonance and could be relevant to the pairing
mechanism.Comment: 4 pages, 4 figures; accepted versio
The role of the cooperative Jahn-Teller effect in the charge ordered La1-xCaxMnO3 (0.5<=x<=0.87) manganites
Based on the magnetoresistance, magnetization, ultrasound, and
crystallographic data, we studied the role of the cooperative Jahn-Teller
effect in the charge ordered (CO) state for La1-xCaxMnO3. We found that, with
increasing the fraction of Q3 mode of Jahn-Teller distortion and decreasing
that of Q2 mode in the CO state, the magnetic structure evolves from CE-type to
C-type and the orbital ordering changes from 3d(x2-r2)/3d(y2-r2)-type to
3d(x2-z2)-type, with the strength of ferromagnetism and the phase separation
tendency being suppressed. At the same time, the stability of the CO state and
the cooperative Jahn-Teller lattice distortion increase. These effects imply
that the cooperative Jahn-Teller effect with different vibration modes is the
key ingredient in understanding the essential physics of the CO state.Comment: 10 pages, 2 figures. To appear on Applied Physics Letter
High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopy
We report optical spectroscopic measurements on electron- and hole-doped
BaFe2As2. We show that the compounds in the normal state are not simple metals.
The optical conductivity spectra contain, in addition to the free carrier
response at low frequency, a temperature-dependent gap-like suppression at
rather high energy scale near 0.6 eV. This suppression evolves with the
As-Fe-As bond angle induced by electron- or hole-doping. Furthermore, the
feature becomes much weaker in the Fe-chalcogenide compounds. We elaborate that
the feature is caused by the strong Hund's rule coupling effect between the
itinerant electrons and localized electron moment arising from the multiple Fe
3d orbitals. Our experiments demonstrate the coexistence of itinerant and
localized electrons in iron-based compounds, which would then lead to a more
comprehensive picture about the metallic magnetism in the materials.Comment: 6 pages, 7 figure
Effect of transition-metal substitution in iron-based superconductors
We study theoretically the current debatable issue about the effect of
transition-metal (TM) substitution in iron-based superconductors through
treating all of the TM ions as randomly distributed impurities. The extra
electrons from TM elements are localized at the impurity sites. In the mean
time the chemical potential shifts upon substitution. The phase diagram is
mapped out and it seems that the TM elements can act as effective dopants. The
local density of states (LDOS) is calculated and the bottom becomes V-shaped as
the impurity concentration increases. The LDOS at the Fermi energy
is finite and reaches the minimum at the optimal doping level.
Our results are in good agreement with the scanning tunneling microscopy
experiments.Comment: 5 pages, 4 figure
Black Hole Decay and Quantum Instantons
We study the analytic structure of the S-matrix which is obtained from the
reduced Wheeler-DeWitt wave function describing spherically symmetric
gravitational collapse of massless scalar fields. The complex simple poles in
the S-matrix lead to the wave functions that satisfy the same boundary
condition as quasi-normal modes of a black hole, and correspond to the bounded
states of the Euclidean Wheeler-DeWitt equation. These wave function are
interpreted as quantum instantons.Comment: RevTex, 7 pages, no figure; The wave functions of gr-qc/9912115 are
newly interpreted as quantum instantons describing a black hole decay.
Replaced by the version to be published in Phys. Rev. D, in which the
boundary condition on the apparent horizon is clarifie
Therapeutic Targeting of TFE3/IRS-1/PI3K/mTOR Axis in Translocation Renal Cell Carcinoma
Purpose: Translocation renal cell carcinoma (tRCC) represents a rare subtype of kidney cancer associated with various TFE3, TFEB, or MITF gene fusions that are not responsive to standard treatments for RCC. Therefore, the identification of new therapeutic targets represents an unmet need for this disease.
Experimental Design: We have established and characterized a tRCC patient-derived xenograft, RP-R07, as a novel preclinical model for drug development by using next-generation sequencing and bioinformatics analysis. We then assessed the therapeutic potential of inhibiting the identified pathway using in vitro and in vivo models.
Results: The presence of a SFPQ-TFE3 fusion [t(X;1) (p11.2; p34)] with chromosomal break-points was identified by RNA-seq and validated by RT-PCR. TFE3 chromatin immunoprecipitation followed by deep sequencing analysis indicated a strong enrichment for the PI3K/AKT/mTOR pathway. Consistently, miRNA microarray analysis also identified PI3K/AKT/mTOR as a highly enriched pathway in RP-R07. Upregulation of PI3/AKT/mTOR pathway in additional TFE3–tRCC models was confirmed by significantly higher expression of phospho-S6 (P < 0.0001) and phospho-4EBP1 (P < 0.0001) in established tRCC cell lines compared with clear cell RCC cells. Simultaneous vertical targeting of both PI3K/AKT and mTOR axis provided a greater antiproliferative effect both in vitro (P < 0.0001) and in vivo (P < 0.01) compared with single-node inhibition. Knockdown of TFE3 in RP-R07 resulted in decreased expression of IRS-1 and inhibited cell proliferation.
Conclusions: These results identify TFE3/IRS-1/PI3K/AKT/mTOR as a potential dysregulated pathway in TFE3–tRCC, and suggest a therapeutic potential of vertical inhibition of this axis by using a dual PI3K/mTOR inhibitor for patients with TFE3–tRCC
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