390 research outputs found
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
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
Tiebout with Politics: Capital Tax Competition and Constitutional Choices.
This paper examines how capital tax competition affects jurisdiction formation. We describe a locational model of public goods provision, where jurisdictions are represented by coalitions of consumers with similar tastes, and where the levels of taxation and local public goods provision within jurisdictions are selected by majority voting. We show that in this setting interjurisdictional tax competition results in an enlargement of jurisdictional boundaries, and can raise welfare for all members of a jurisdiction even in the absence of intrajurisdictional transfers.
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
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
Stochastic dynamics for a single vibrational mode in molecular junctions
We propose a very accurate computational scheme for the dynamics of a
classical oscillator coupled to a molecular junction driven by a finite bias,
including the finite mass effect. We focus on two minimal models for the
molecular junction: Anderson-Holstein (AH) and two-site Su-Schrieffer-Heeger
(SSH) models. As concerns the oscillator dynamics, we are able to recover a
Langevin equation confirming what found by other authors with different
approaches and assessing that quantum effects come from the electronic
subsystem only. Solving numerically the stochastic equation, we study the
position and velocity distribution probabilities of the oscillator and the
electronic transport properties at arbitrary values of electron-oscillator
interaction, gate and bias voltages. The range of validity of the adiabatic
approximation is established in a systematic way by analyzing the behaviour of
the kinetic energy of the oscillator. Due to the dynamical fluctuations, at
intermediate bias voltages, the velocity distributions deviate from a gaussian
shape and the average kinetic energy shows a non monotonic behaviour. In this
same regime of parameters, the dynamical effects favour the conduction far from
electronic resonances where small currents are observed in the infinite mass
approximation. These effects are enhanced in the two-site SSH model due to the
presence of the intermolecular hopping t. Remarkably, for sufficiently large
hopping with respect to tunneling on the molecule, small interaction strengths
and at intermediate bias (non gaussian regime), we point out a correspondence
between the minima of the kinetic energy and the maxima of the dynamical
conductance.Comment: 19 pages, 16 figures, submitted to Physical Review
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