3,666 research outputs found
Effect of van-Hove singularities in single-walled carbon nanotube leads on transport through double quantum dot system
The double quantum dot system with single-walled metallic armchair carbon
nanotube leads has been studied using Non-equilibrium Green function in the
Keldysh formalism. The effect of relative spacing between the energy levels of
the dots, interdot tunneling matrix-element, interdot Coulomb interaction and
van-Hove singularities in density of states characteristics of
quasi-one-dimensional carbon nanotube leads on the conductance of the double
quantum dot system has been studied. The conductance and dot occupancies are
calculated at finite temperature. It is observed that the density of states of
the carbon nanotube leads play a significant role in determining the
conductance profile. In particular, whenever the chemical potential of the
isolated double quantum dot system is aligned with the position of a van-Hove
singularity in the density of states of armchair carbon nanotube leads, the
height of the corresponding conductance peak falls considerably. It is further
observed that the suppression in the heights of the alternate peaks depends on
the relative positions of the energy levels of the dots and their magnitude of
separation.Comment: 16 pages and 16 figure
Breathing Modes in Rotating Bose-Condensed Gas: An Exact Diagonalization Study
We present an exact diagonalization study of the breathing mode collective
excitations for a rotating Bose-Einstein condensate of spinless bosons
interacting via repulsive finite-range Gaussian potential and harmonically
confined in quasi-two-dimension. The yrast state and the low-lying excited
states are variationally obtained in given subspaces of the quantized total
angular momentum employing the beyond lowest Landau level approximation in
slowly rotating regime with . For a given , the low-energy
eigenspectra (bands) are obtained in weakly to moderately interacting regime.
Further, for a given interaction, the split in low-lying eigenenergies with
increasing is the precursor to spontaneous symmetry breaking of the
axisymmetry associated with the entry of the first vortex. With increase in
repulsive interaction, the value of the first breathing mode increases for
stable total angular momentum states L=0~\mbox{and}~N, but decreases for
intermediate metastable states. The position of the observed first
breathing modes in the eigenspectrum remains unchanged as the interaction is
varied over several orders of magnitude.Comment: 5 pages, 3 figures, RevTex two colum
Model of the optical emission of a driven semiconductor quantum dot: phonon-enhanced coherent scattering and off-resonant sideband narrowing
We study the crucial role played by the solid-state environment in
determining the photon emission characteristics of a driven quantum dot. For
resonant driving, we predict a phonon-enhancement of the coherently emitted
radiation field with increasing driving strength, in stark contrast to the
conventional expectation of a rapidly decreasing fraction of coherent emission
with stronger driving. This surprising behaviour results from thermalisation of
the dot with respect to the phonon bath, and leads to a nonstandard regime of
resonance fluorescence in which significant coherent scattering and the Mollow
triplet coexist. Off-resonance, we show that despite the phonon influence,
narrowing of dot spectral sideband widths can occur in certain regimes,
consistent with an experimental trend.Comment: Published version. 5 pages, 2 figures, plus 4 page supplement. Title
changed, figure 1 revised, various edits and additions to the tex
Anticrossings in Foerster Coupled Quantum Dots
We consider two coupled generic quantum dots, each modelled by a simple
potential which allows the derivation of an analytical expression for the
inter-dot Foerster coupling, in the dipole-dipole approximation. We investigate
the energy level behaviour of this coupled two-dot system under the influence
of an external applied electric field and predict the presence of anticrossings
in the optical spectra due to the Foerster interaction.Comment: 13 pages, 7 figures. Published version. Substantially revised, new
sections on decay rates, absorption spectra, and tunnelin
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