443 research outputs found
Invaded Cluster Dynamics for Frustrated Models
The Invaded Cluster (IC) dynamics introduced by Machta et al. [Phys. Rev.
Lett. 75 2792 (1995)] is extended to the fully frustrated Ising model on a
square lattice. The properties of the dynamics which exhibits numerical
evidence of self-organized criticality are studied. The fluctuations in the IC
dynamics are shown to be intrinsic of the algorithm and the
fluctuation-dissipation theorem is no more valid. The relaxation time is found
very short and does not present critical size dependence.Comment: notes and refernences added, some minor changes in text and fig.3,5,7
16 pages, Latex, 8 EPS figures, submitted to Phys. Rev.
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
Electron-vibration effects on the thermoelectric efficiency of molecular junctions
The thermoelectric properties of a molecular junction model, appropriate for
large molecules such as fullerenes, are studied within a non-equilibrium
adiabatic approach in the linear regime at room temperature. A self-consistent
calculation is implemented for electron and phonon thermal conductance showing
that both increase with the inclusion of the electron-vibration coupling.
Moreover, we show that the deviations from the Wiedemann-Franz law are
progressively reduced upon increasing the interaction between electronic and
vibrational degrees of freedom. Consequently, the junction thermoelectric
efficiency is substantially reduced by the electron-vibration coupling. Even
so, for realistic parameters values, the thermoelectric figure of merit can
still have peaks of the order of unity. Finally, in the off-resonant electronic
regime, our results are compared with those of an approach which is exact for
low molecular electron densities. We give evidence that in this case additional
quantum effects, not included in the first part of this work, do not affect
significantly the junction thermoelectric properties in any temperature regime.Comment: 15 pages, 11 figures, 2 Appendice
Single-parameter adiabatic charge pumping in carbon nanotube resonators
Single-parameter adiabatic charge pumping, induced by a nearby
radio-frequency antenna, is achieved in suspended carbon nanotubes close to the
mechanical resonance. The charge pumping is due to an important dynamic
adjustment of the oscillating motion to the antenna signal and it is different
from the mechanism active in the two-parameter pumping. Finally, the second
harmonic oscillator response shows an interesting relationship with the first
harmonic that should be experimentally observed
Plasmons in topological insulator cylindrical nanowires
We present a theoretical analysis of Dirac magneto-plasmons in topological
insulator nanowires. We discuss a cylindrical geometry where Berry phase
effects induce the opening of a gap at the neutrality point. By taking into
account surface electron wave functions introduced in previous papers and
within the random phase approximation, we provide an analytical form of the
dynamic structure factor. Dispersions and spectral weights of Dirac plasmons
are studied with varying the radius of the cylinder, the surface doping, and
the strength of an external magnetic field. We show that, at zero surface
doping, inter-band damped plasmon-like excitations form at the surface and
survive at low electron surface dopings (). Then, we
point out that the plasmon excitations are sensitive to the Berry phase gap
closure when an external magnetic field close to half quantum flux is
introduced. Indeed, a well-defined magneto-plasmon peak is observed at lower
energies upon the application of the magnetic field. Finally, the increase of
the surface doping induces a crossover from damped inter-band to sharp
intra-band magneto-plasmons which, as expected for large radii and dopings
(), approach the proper limit of a two-dimensional
surface.Comment: 18 pages, 11 figures, 2 Appendice
Interplay between electron-electron and electron-vibration interactions on the thermoelectric properties of molecular junctions
The linear thermoelectric properties of molecular junctions are theoretically
studied close to room temperature within a model including electron-electron
and electron-vibration interactions on the molecule. A nonequilibrium adiabatic
approach is generalized to include large Coulomb repulsion through a
self-consistent procedure and applied to the investigation of large molecules,
such as fullerenes, within the Coulomb blockade regime. The focus is on the
phonon thermal conductance which is quite sensitive to the effects of strong
electron-electron interactions within the intermediate electron-vibration
coupling regime. The electron-vibration interaction enhances the phonon and
electron thermal conductance, and it reduces the charge conductance and the
thermopower inducing a decrease of the thermoelectric figure of merit. For
realistic values of junction parameters, the peak values of the thermoelectric
figure of merit are still of the order of unity since the phonon thermal
conductance can be even smaller than the electron counterpart.Comment: 8 pages, 1 Appendix, 12 pages. arXiv admin note: substantial text
overlap with arXiv:1406.377
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
Effects of electron-phonon coupling range on the polaron formation
The polaron features due to electron-phonon interactions with different
coupling ranges are investigated by adopting a variational approach. The
ground-state energy, the spectral weight, the average kinetic energy, the mean
number of phonons, and the electron-lattice correlation function are discussed
for the system with coupling to local and nearest neighbor lattice
displacements comparing the results with the long range case. For large values
of the coupling with nearest neighbor sites, most physical quantities show a
strong resemblance with those obtained for the long range electron-phonon
interaction. Moreover, for intermediate values of interaction strength, the
correlation function between electron and nearest neighbor lattice
displacements is characterized by an upturn as function of the electron-phonon
coupling constant.Comment: 5 pages and 4 figure
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