111 research outputs found
Electron Correlations in a Quantum Dot with Bychkov-Rashba Coupling
We report on a theoretical approach developed to investigate the influence of
Bychkov-Rashba interaction on a few interacting electrons confined in a quantum
dot. We note that the spin-orbit coupling profoundly influences the energy
spectrum of interacting electrons in a quantum dot. Inter-electron interaction
causes level crossings in the ground state and a jump in magnetization. As the
coupling strength is increased, that jump is shifted to lower magnetic fields.
Low-field magnetization will therefore provide a direct probe of the spin-orbit
coupling strength in a quantum dot
Interacting Dark Resonances: Interference Effects Induced by Coherently Altered Quantum Superpositions
We predict the possibility of sharp, high-contrast resonances in the optical
response of a broad class of systems, wherein interference effects are
generated by coherent perturbation or interaction of dark states. The
properties of these resonances can be manipulated to design a desired atomic
response.Comment: 4 pages, 3 figures, RevTeX, submitted to PRL; changed three numbers
in Fig. 3 (caption
Orthogonality catastrophe in a one-dimensional system of correlated electrons
We present a detailed numerical study of the orthogonality catastrophe
exponent for a one-dimensional lattice model of spinless fermions with nearest
neighbor interaction using the density matrix remormalization group algorithm.
Keeping up to 1200 states per block we achieve a very great accuracy for the
overlap which is needed to extract the orthogonality exponent reliably. We
discuss the behavior of the exponent for three different kinds of a localized
impurity. For comparison we also discuss the non-interacting case. In the weak
impurity limit our results for the overlap confirm scaling behavior expected
from perturbation theory and renormalization group calculations. In particular
we find that a weak backward scattering component of the orthogonality exponent
scales to zero for attractive interaction. In the strong impurity limit and for
repulsive interaction we demonstrate that the orthogonality exponent cannot be
extracted from the overlap for systems with up to 100 sites, due to finite size
effects. This is in contradiction to an earlier interpretation given by Qin et
al. based on numerical data for much smaller system sizes. Neverthless we find
indirect evidence that the backward scattering contribution to the exponent
scales to 1/16 based on predictions of boundary conformal field theory.Comment: 16 pages, Latex, 8 eps figures, submitted to Phys. Rev.
Mesoscopic fluctuations of the ground state spin of a small metal particle
We study the statistical distribution of the ground state spin for an
ensemble of small metallic grains, using a random-matrix toy model. Using the
Hartree Fock approximation, we find that already for interaction strengths well
below the Stoner criterion there is an appreciable probability that the ground
state has a finite, nonzero spin. Possible relations to experiments are
discussed.Comment: 4 pages, RevTeX; 1 figure included with eps
Transport Properties of Multiple Quantum Dots Arranged in Parallel: Results from the Bethe Ansatz
In this paper we analyze transport through a double dot system connected to
two external leads. Imagining each dot possessing a single active level, we
model the system through a generalization of the Anderson model. We argue that
this model is exactly solvable when certain constraints are placed upon the dot
Coulomb charging energy, the dot-lead hybridization, and the value of the
applied gate voltage. Using this exact solvability, we access the zero
temperature linear response conductance both in and out of the presence of a
Zeeman field. We are also able to study the finite temperature linear response
conductance. We focus on universal behaviour and identify three primary
features in the transport of the dots: i) a so-called RKKY Kondo effect; ii) a
standard Kondo effect; and iii) interference phenomena leading to sharp
variations in the conductance including conductance zeros. We are able to use
the exact solvability of the dot model to characterize these phenomena
quantitatively. While here we primarily consider a double dot system, the
approach adopted applies equally well to N-dot systems.Comment: 28 pages, 10 figures; references added in v
Interference effects in interacting quantum dots
In this paper we study the interplay between interference effects in quantum
dots (manifested through the appearance of Fano resonances in the conductance),
and interactions taken into account in the self-consistent Hartree-Fock
approximation. In the non-interacting case we find that interference may lead
to the observation of more than one conductance peak per dot level as a
function of an applied gate voltage. This may explain recent experimental
findings, which were thought to be caused by interaction effects. For the
interacting case we find a wide variety of different interesting phenomena.
These include both monotonous and non-monotonous filling of the dot levels as a
function of an applied gate voltage, which may occur continuously or even
discontinuously. In many cases a combination of the different effects can occur
in the same sample. The behavior of the population influences, in turn, the
conductance lineshape, causing broadening and asymmetry of narrow peaks, and
determining whether there will be a zero transmission point. We elucidate the
essential role of the interference between the dot levels in determining these
outcomes. The effects of finite temperatures on the results are also examined.Comment: 11 pages, 9 fugures, REVTeX
Impurity in a Luttinger liquid away from half-filling: a numerical study
Conformal field theory gives quite detailed predictions for the low energy
spectrum and scaling exponents of a massless Luttinger liquid at generic
filling in the presence of an impurity. While these predictions were verified
for half-filled systems, there was till now no analysis away from this
particular filling. Here, we fill in this gap by numerically investigating a
quarter-filled system using the density matrix renormalization group technique.
Our results confirm conformal field theory predictions, and suggest that they
are indeed valid for arbitrary fillings.Comment: 9 pages (include figures), one reference added in this new versio
A stationary source of non-classical or entangled atoms
A scheme for generating continuous beams of atoms in non-classical or
entangled quantum states is proposed and analyzed. For this the recently
suggested transfer technique of quantum states from light fields to collective
atomic excitation by Stimulated Raman adiabatic passage [M.Fleischhauer and
M.D. Lukin, Phys.Rev.Lett. 84, 5094 (2000)] is employed and extended to matter
waves
Transport theory of carbon nanotube Y junctions
We describe a generalization of Landauer-B\"uttiker theory for networks of
interacting metallic carbon nanotubes. We start with symmetric starlike
junctions and then extend our approach to asymmetric systems. While the
symmetric case is solved in closed form, the asymmetric situation is treated by
a mix of perturbative and non-perturbative methods. For N>2 repulsively
interacting nanotubes, the only stable fixed point of the symmetric system
corresponds to an isolated node. Detailed results for both symmetric and
asymmetric systems are shown for N=3, corresponding to carbon nanotube Y
junctions.Comment: submitted to New Journal of Physics, Focus Issue on Carbon Nanotubes,
15 pages, 3 figure
Experimental Evidence for Resonant-Tunneling in a Luttinger-Liquid
We have measured the low temperature conductance of a one-dimensional island
embedded in a single mode quantum wire. The quantum wire is fabricated using
the cleaved edge overgrowth technique and the tunneling is through a single
state of the island. Our results show that while the resonance line shape fits
the derivative of the Fermi function the intrinsic line width decreases in a
power law fashion as the temperature is reduced. This behavior agrees
quantitatively with Furusaki's model for resonant tunneling in a
Luttinger-liquid.Comment: 3 pages, 5 figures, corrected typo
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