270 research outputs found
Nonlocal Excitations and 1/8 Singularity in Cuprates
Momentum-dependent excitation spectra of the two-dimensional Hubbard model on
the square lattice have been investigated at zero temperature on the basis of
the full self-consistent projection operator method in order to clarify
nonlocal effects of electron correlations on the spectra. It is found that
intersite antiferromagnetic correlations cause shadow bands and enhance the
Mott-Hubbard splittings near the half-filling. Furthermore nonlocal excitations
are shown to move the critical doping concentration , at
which the singular quasiparticle peak is located just on the Fermi level, from
(the single-site value) to .
The latter suggests the occurance of an instability such as the stripe at
.Comment: 4 pages, 5 figures; to be published in the Journal of Korean Physical
Society (ICM12
Local-Ansatz Approach with Momentum Dependent Variational Parameters to Correlated Electron Systems
A new wavefunction which improves the Gutzwiller-type local ansatz method has
been proposed to describe the correlated electron system. The ground-state
energy, double occupation number, momentum distribution function, and
quasiparticle weight have been calculated for the half-filled band Hubbard
model in infinite dimensions. It is shown that the new wavefunction improves
the local-ansatz approach (LA) proposed by Stollhoff and Fulde. Especially,
calculated momentum distribution functions show a reasonable momentum
dependence. The result qualitatively differs from those obtained by the LA and
the Gutzwiller wavefunction. Furthermore, the present approach combined with
the projection operator method CPA is shown to describe quantitatively the
excitation spectra in the insulator regime as well as the critical Coulomb
interactions for a gap formation in infinite dimensions.Comment: To be published in Phys. Soc. Jpn. 77 No.11 (2008
Kink Structure in the Quasiparticle Band of Doped Hubbard Systems
By making use of the self-consistent projection operator method with
high-momentum and high-energy resolutions, we find a kink structure in the
quasiparticle excitation spectrum of the two-dimensional Hubbard model in the
underdoped regime. The kink is caused by a mixing between the quasiparticle
state and excitations with short-range antiferromagnetic order. We suggest that
this might be the origin of the strong concentration dependence of the 'kink'
found in La_{2-x}Sr_{x}CuO_{4} (x=0.03-0.07).Comment: 3 pages, 4 figures. to be published in J. Phys. Soc. Jpn., Vol. 74,
No. 9, September 15, 200
First-Principles Dynamical Coherent-Potential Approximation Approach to the Ferromagnetism of Fe, Co, and Ni
Magnetic properties of Fe, Co, and Ni at finite temperatures have been
investigated on the basis of the first-principles dynamical CPA (Coherent
Potential Approximation) combined with the LDA (Local Density Approximation) +
Hamiltonian in the Tight-Binding Linear Muffintin Orbital (TB-LMTO)
representation. The Hamiltonian includes the transverse spin fluctuation terms.
Numerical calculations have been performed within the harmonic approximation
with 4th-order dynamical corrections. Calculated single-particle densities of
states in the ferromagnetic state indicate that the dynamical effects reduce
the exchange splitting, suppress the band width of the quasi-particle state,
and causes incoherent excitations corresponding the 6 eV satellites. Results of
the magnetization vs temperature curves, paramagnetic spin susceptibilities,
and the amplitudes of local moments are presented. Calculated Curie
temperatures () are reported to be 1930K for Fe, 2550K for Co, and
620K for Ni; for Fe and Co are overestimated by a factor of 1.8,
while in Ni agrees with the experimental result. Effective Bohr
magneton numbers calculated from the inverse susceptibilities are 3.0 (Fe), 3.0 (Co), and 1.6 (Ni), being in
agreement with the experimental ones. Overestimate of in Fe and Co
is attributed to the neglects of the higher-order dynamical effects as well as
the magnetic short range order.Comment: 10 pages, 13 figure
Evidence of Strong Electron Correlations in Gamma-Iron
Single-particle excitation spectra of gamma-Fe in the paramagnetic state have
been investigated by means of the first-principles dynamical coherent potential
approximation theory which has recently been developed. It is found that the
central peak in the density of states consisting of the t2g bands is destroyed
by electron correlations, and the Mott-Hubbard type correlated bands appear.
The results indicate that the gamma-Fe can behave as correlated electrons at
high temperatures.Comment: 7 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Vol.78,
No.9 (2009
Enhanced Urinary Bladder, Liver and Colon Carcinogenesis in Zucker Diabetic Fatty Rats in a Multiorgan Carcinogenesis Bioassay: Evidence for Mechanisms Involving Activation of PI3K Signaling and Impairment of p53 on Urinary Bladder Carcinogenesis
In the present study, modifying effects of diabetes on carcinogenesis induced in type 2
diabetes mellitus model Zucker diabetic fatty (ZDF) rats were investigated using a
multiorgan carcinogenesis bioassay. Our re sults demonstrated enhancement of urinary
bladder, colon and liver carcinogenesis in ZDF rats treated with five types of carcinogens
(DMBDD). Elevated insulin and leptin and decreased adiponectin levels in the serum may be
responsible for the high susceptibility of type 2 diabetes mellitus model rats to
carcinogenesis in these organs. Possible mechanisms of increased susceptibility of
diabetic rats to bladder carcinogenesis could be activation of the PI3K pathway and
suppression of p53 in the urothelium in consequence of the above serum protein
alterations
On-site correlation in valence and core states of ferromagnetic nickel
We present a method which allows to include narrow-band correlation effects
into the description of both valence and core states and we apply it to the
prototypical case of nickel. The results of an ab-initio band calculation are
used as input mean-field eigenstates for the calculation of self-energy
corrections and spectral functions according to a three-body scattering
solution of a multi-orbital Hubbard hamiltonian. The calculated quasi-particle
spectra show a remarkable agreement with photoemission data in terms of band
width, exchange splitting, satellite energy position of valence states, spin
polarization of both the main line and the satellite of the 3p core level.Comment: 14 pages, 10 PostScript figures, RevTeX, submitted to PR
Magnetic properties of X-Pt (X=Fe,Co,Ni) alloy systems
We have studied the electronic and magnetic properties of Fe-Pt, Co-Pt and
Ni-Pt alloy systems in ordered and disordered phases. The influence of various
exchange-correlation functionals on values of equilibrium lattice parameters
and magnetic moments in ordered Fe-Pt, Co-Pt and Ni-Pt alloys have been studied
using linearized muffin-tin orbital method. The electronic structure
calculations for the disordered alloys have been carried out using augmented
space recursion technique in the framework of tight binding linearized
muffin-tin orbital method. The effect of short range order has also been
studied in the disordered phase of these systems. The results show good
agreements with available experimental values.Comment: 21 pages, 4 eps figures, accepted for publication in Journal of
Physics Condensed Matte
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