6,872 research outputs found
Normal state properties of an interacting large polaron gas
A simple approach to the many-polaron problem for both weak and intermediate
electron-phonon coupling and valid for densities much smaller than those
typical of metals is presented. Within the model the total energy, the
collective modes and the single-particle properties are studied and compared
with the available theories. It is shown the occurrence of a charge density
wave instability in the intermediate coupling regime.Comment: 26 pages, 12 figures. To appear on European Physical Journal
Optical properties of an interacting large polaron gas
The normal state conductivity of a system of interacting large polarons is
calculated within the Random Phase approximation and some numerical results are
presented. The behaviour of the optical absorption as a function of the charge
carrier density and of the temperature is analyzed for different values of the
electron-phonon coupling constant. It is shown that the conductivity exihibits
features similar to thos observed in the infrared spectra of the cuprates.Comment: 13 pages, 1 table, 3 figures (to be published ob Eur. Jour. Phys. B
Spectral properties and infrared absorption in manganites
Within a recently proposed variational approach it has been shown that, in
perovskites with , near the metal-insulator
transition, the combined effect of the magnetic and electron-phonon
interactions pushes the system toward a regime of two coexisting phases: a low
electron density one made by itinerant large polarons forming ferromagnetic
domains and a high electron density one made by localized small polarons giving
rise to paramagnetic or antiferromagnetic domains depending on temperature.
Employing the above-mentioned variational scheme, in this paper spectral and
optical properties of manganites are derived for at different
temperatures. It is found that the phase separation regime induces a robust
pseudogap in the excitation spectrum of the system. Then the conductivity
spectra are characterized by a transfer of spectral weight from high to low
energies, as the temperature decreases. In the metallic ferromagnetic
phase, at low two types of infrared absorption come out: a Drude term and a
broad absorption band due respectively to the coherent and incoherent motion of
large polarons. The obtained results turn out in good agreement with
experiments.Comment: 9 figure
On the interface polaron formation in organic field-effect transistors
A model describing the low density carrier state in an organic single crystal
FET with high- gate dielectrics is studied. The interplay between
charge carrier coupling with inter-molecular vibrations in the bulk of the
organic material and the long-range interaction induced at the interface with a
polar dielectric is investigated. This interplay is responsible for the
stabilization of a polaronic state with an internal structure extending on few
lattice sites, at much lower coupling strengths than expected from the polar
interaction alone. This effect could give rise to polaron self-trapping in
high- organic FET's without invoking unphysically large values of the
carrier interface interaction.Comment: 9 pages, 9 figure
Non-local composite spin-lattice polarons in high temperature superconductors
The non-local nature of the polaron formation in t-t'-t"-J model is studied
in large lattices up to 64 sites by developing a new numerical method. We show
that the effect of longer-range hoppings t' and t" is a large anisotropy of the
electron-phonon interaction (EPI) leading to a completely different influence
of EPI on the nodal and antinodal points in agreement with the experiments.
Furthermore, nonlocal EPI preserves polaron's quantum motion, which destroys
the antiferromagnetic order effectively, even at strong coupling regime,
although the quasi-particle weight in angle-resolved-photoemission spectroscopy
is strongly suppressed.Comment: 5 pages, 4 figure
Temperature dependence of the angle resolved photoemission spectra in the undoped cuprates: self-consistent approach to the t-J-Holstein model
We develop a novel self-consistent approach for studying the angle resolved
photoemission spectra (ARPES) of a hole in the t-J-Holstein model giving
perfect agreement with numerically exact Diagrammatic Monte Carlo data at zero
temperature for all regimes of electron-phonon coupling. Generalizing the
approach to finite temperatures we find that the anomalous temperature
dependence of the ARPES in undoped cuprates is explained by cooperative
interplay of coupling of the hole to magnetic fluctuations and strong
electron-phonon interaction.Comment: 5 pages, 4 figure
Steps toward a classifier for the Virtual Observatory. I. Classifying the SDSS photometric archive
Modern photometric multiband digital surveys produce large amounts of data
that, in order to be effectively exploited, need automatic tools capable to
extract from photometric data an objective classification. We present here a
new method for classifying objects in large multi-parametric photometric data
bases, consisting of a combination of a clustering algorithm and a cluster
agglomeration tool. The generalization capabilities and the potentialities of
this approach are tested against the complexity of the Sloan Digital Sky Survey
archive, for which an example of application is reported.Comment: To appear in the Proceedings of the "1st Workshop of Astronomy and
Astrophysics for Students" - Naples, 19-20 April 200
Ballistic transport in one-dimensional loops with Rashba and Dresselhaus spin-orbit coupling
We discuss the combined effect of Rashba and Dresselhaus spin-orbit
interactions in polygonal loops formed by quantum wires, when the electron are
injected in a node and collected at the opposite one. The conditions that allow
perfect localization are found. Furthermore, we investigate the suppression of
the Al'tshuler--Aronov--Spivak oscillations that appear, in presence of a
magnetic flux, when the electrons are injected and collected at the same node.
Finally, we point out that a recent realization of a ballistic spin
interferometer can be used to obtain a reliable estimate of the magnitude ratio
of the two spin-orbit interactions.\bigskipComment: 6 figure
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