1,366 research outputs found
Stability analysis of some integrable Euler equations for SO(n)
A family of special cases of the integrable Euler equations on
introduced by Manakov in 1976 is considered. The equilibrium points are found
and their stability is studied. Heteroclinic orbits are constructed that
connect unstable equilibria and are given by the orbits of certain 1-parameter
subgroups of SO(n). The results are complete in the case and incomplete
for .Comment: 15 pages, LaTeX, minor stylistic changes in v
Distribution of localized states from fine analysis of electron spin resonance spectra of organic semiconductors: Physical meaning and methodology
We develop an analytical method for the processing of electron spin resonance
(ESR) spectra. The goal is to obtain the distributions of trapped carriers over
both their degree of localization and their binding energy in semiconductor
crystals or films composed of regularly aligned organic molecules [Phys. Rev.
Lett. v. 104, 056602 (2010)]. Our method has two steps. We first carry out a
fine analysis of the shape of the ESR spectra due to the trapped carriers; this
reveals the distribution of the trap density of the states over the degree of
localization. This analysis is based on the reasonable assumption that the
linewidth of the trapped carriers is predetermined by their degree of
localization because of the hyperfine mechanism. We then transform the
distribution over the degree of localization into a distribution over the
binding energies. The transformation uses the relationships between the binding
energies and the localization parameters of the trapped carriers. The
particular relation for the system under study is obtained by the Holstein
model for trapped polarons using a diagrammatic Monte Carlo analysis. We
illustrate the application of the method to pentacene organic thin-film
transistors.Comment: 14 pages, 11 figure
Polaron in t-J model
We present numeric results for ground state and angle resolved photoemission
spectra (ARPES) for single hole in t-J model coupled to optical phonons. The
systematic-error free diagrammatic Monte Carlo is employed where the Feynman
graphs for the Matsubara Green function in imaginary time are summed up
completely with respect to phonons variables, while magnetic variables are
subjected to non-crossing approximation. We obtain that at electron-phonon
coupling constants relevant for high Tc cuprates the polaron undergoes
self-trapping crossover to strong coupling limit and theoretical ARPES
demonstrate features observed in experiment: a broad peak in the bottom of the
spectra has momentum dependence which coincides with that of hole in pure t-J
model.Comment: 4 pages, 4 figure
Charge response function and a novel plasmon mode in graphene
Polarizability of non-interacting 2D Dirac electrons has a 1/\sqrt{qv-\omega}
singularity at the boundary of electron-hole excitations. The screening of this
singularity by long-range electron-electron interactions is usually treated
within the random phase approximation. The latter is exact only in the limit of
N -> infinity, where N is the ``color'' degeneracy. We find that the
ladder-type vertex corrections become crucial close to the threshold as the
ratio of the n-th order ladder term to the same order RPA contribution is
(\ln|qv-\omega|)^n/N^n$. We perform analytical summation of the infinite series
of ladder diagrams which describe excitonic effect. Beyond the threshold,
qv>\omega, the real part of the polarization operator is found to be positive
leading to the appearance of a strong and narrow plasmon resonance.Comment: 4 pages, 3 figures,typos correcte
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