467 research outputs found
Electron dynamics in the normal state of cuprates: spectral function, Fermi surface and ARPES data
An influence of the electron-phonon interaction on excitation spectrum and
damping in a narrow band electron subsystem of cuprates has been investigated.
Within the framework of the t-J model an approach to solving a problem of
account of both strong electron correlations and local electron-phonon binding
with characteristic Einstein mode in the normal state has been
presented. In approximation Hubbard-I it was found an exact solution to the
polaron bands. We established that in the low-dimensional system with a pure
kinematic part of Hamiltonian a complicated excitation spectrum is realized. It
is determined mainly by peculiarities of the lattice Green's function. In the
definite area of the electron concentration and hopping integrals a correlation
gap may be possible on the Fermi level. Also, in specific cases it is observed
a doping evolution of the Fermi surface. We found that the strong
electron-phonon binding enforces a degree of coherence of electron-polaron
excitations near the Fermi level and spectrum along the nodal direction depends
on wave vector module weakly. It corresponds to ARPES data. A possible origin
of the experimentally observed kink in the nodal direction of cuprates is
explained by fine structure of the polaron band to be formed near the mode
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Diagrammatic method for theory of magnetic and resistive properties of manganites
Effective field theory of magnetic and resistive properties of manganites
with account of strong Hund exchange coupling and electron-phonon interactions
has been evolved under the strong Hund coupling condition. In parallel with
Lang-Firsov unitary transformation of the zeroth Hamiltonian, we have realized
the diagonalization of Hund's Hamiltonian neglecting the upper triplet. The
diagram techniques taking into account the quantum spin fluctuations of lower
quintet and hole state with spin S=3/2 was developed. The magnetic structure of
the ground state and an influence of electron-phonon interaction have been
analyzed using the first nonvanishing approximation of perturbation theory. The
calculated temperature dependence of resistivity agrees well with experimental
data including these obtained in applied magnetic field.Comment: 44 pages, 14 figure
Pauli-Villars Regularization in nonperturbative Hamiltonian approach on the Light Front
The advantage of Pauli-Villars regularization in quantum field theory
quantized on the light front is explained. Simple examples of scalar
field theory and Yukawa-type model are used. We give also an
example of nonperturbative calculation in the theory with Pauli-Villars fields,
using for that a model of anharmonic oscillator modified by inclusion of ghost
variables playing the role similar to Pauli-Villars fields.Comment: LaTeX, 10 pages, 2 figures. Article will be published in AIP
Conference Proceedings, the final publication will be available at
http://scitation.aip.org/content/aip/proceeding/aipc
Chemistry-climate model SOCOL: a validation of the present-day climatology
International audienceIn this paper we document ''SOCOL'', a new chemistry-climate model, which has been ported for regular PCs and shows good wall-clock performance. An extensive validation of the model results against present-day climate obtained from observations and assimilation data sets shows that the model describes the climatological state of the atmosphere for the late 1990s with reasonable accuracy. The model has a significant temperature bias only in the upper stratosphere and near the tropopause in the tropics and high latitudes. The latter is the result of the rather low vertical resolution of the model near the tropopause. The former can be attributed to a crude representation of the radiation heating in the middle atmosphere. A comparison of the simulated and observed link between the tropical stratospheric structure and the strength of the polar vortex shows that in general, both observations and simulations reveal a higher temperature and ozone mixing ratio in the lower tropical stratosphere for the case with stronger Polar night jet (PNJ) as predicted by theoretical studies
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