128 research outputs found
Effective action and interaction energy of coupled quantum dots
We obtain the effective action of tunnel-coupled quantum dots, by modeling
the system as a Luttinger liquid with multiple barriers. For a double dot
system, we find that the resonance conditions for perfect conductance form a
hexagon in the plane of the two gate voltages controlling the density of
electrons in each dot. We also explicitly obtain the functional dependence of
the interaction energy and peak-splitting on the gate voltage controlling
tunneling between the dots and their charging energies. Our results are in good
agreement with recent experimental results, from which we obtain the Luttinger
interaction parameter .Comment: 5 pgs,latex,3 figs,revised version to be publshed in Phys.Rev.
Strong Tunneling in Double-Island Structures
We study the electron transport through a system of two low-capacitance metal
islands connected in series between two electrodes. The work is motivated in
part by experiments on semiconducting double-dots, which show intriguing
effects arising from coherent tunneling of electrons and mixing of the
single-electron states across tunneling barriers. In this article, we show how
coherent tunneling affects metallic systems and leads to a mixing of the
macroscopic charge states across the barriers. We apply a recently formulated
RG approach to examine the linear response of the system with high tunnel
conductances (up to 8e^2/h). In addition we calculate the (second order)
cotunneling contributions to the non-linear conductance. Our main results are
that the peaks in the linear and nonlinear conductance as a function of the
gate voltage are reduced and broadened in an asymmetric way, as well as shifted
in their positions. In the limit where the two islands are coupled weakly to
the electrodes, we compare to theoretical results obtained by Golden and
Halperin and Matveev et al. In the opposite case when the two islands are
coupled more strongly to the leads than to each other, the peaks are found to
shift, in qualitative agreement with the recent prediction of Andrei et al. for
a similar double-dot system which exhibits a phase transition.Comment: 12 page
Coulomb Blockade of Tunneling Through a Double Quantum Dot
We study the Coulomb blockade of tunneling through a double quantum dot. The
temperature dependence of the linear conductance is strongly affected by the
inter-dot tunneling. As the tunneling grows, a crossover from
temperature-independent peak conductance to a power-law suppression of
conductance at low temperatures is predicted. This suppression is a
manifestation of the Anderson orthogonality catastrophe associated with the
charge re-distribution between the dots, which accompanies the tunneling of an
electron into a dot. We find analytically the shapes of the Coulomb blockade
peaks in conductance as a function of gate voltage.Comment: 11 pages, revtex3.0 and multicols.sty, 4 figures uuencode
Coulomb blockade of strongly coupled quantum dots studied via bosonization of a channel with a finite barrier
A pair of quantum dots, coupled through a point contact, can exhibit Coulomb
blockade effects that reflect an oscillatory term in the dots' total energy
whose value depends on whether the total number of electrons on the dots is
even or odd. The effective energy associated with this even-odd alternation is
reduced, relative to the bare Coulomb blockade energy for uncoupled dots, by a
factor (1-f) that decreases as the interdot coupling is increased. When the
transmission coefficient for interdot electronic motion is independent of
energy and the same for all channels within the point contact (which are
assumed uncoupled), the factor (1-f) takes on a universal value determined
solely by the number of channels and the dimensionless conductance g of each
individual channel.
This paper studies corrections to the universal value of (1-f) that result
when the transmission coefficent varies over energy scales of the size of the
bare Coulomb blockade energy. We consider a model in which the point contact is
described by a single orbital channel containing a parabolic barrier potential,
and we calculate the leading correction to (1-f) for one-channel (spin-split)
and two-channel (spin-degenerate) point contacts in the limit where the single
orbital channel is almost completely open. By generalizing a previously used
bosonization technique, we find that, for a given value of the dimensionless
conductance g, the value of (1-f) is increased relative to its value for a
zero-thickness barrier, but the absolute value of the increase is small in the
region where our calculations apply.Comment: 13 pages, 3 Postscript figure
Statistics of Wave Functions in Coupled Chaotic Systems
Using the supersymmetry technique, we calculate the joint distribution of
local densities of electron wavefunctions in two coupled disordered or chaotic
quantum billiards. We find novel spatial correlations that are absent in a
single chaotic system. Our exact result can be interpreted for small coupling
in terms of the hybridization of eigenstates of the isolated billiards. We show
that the presented picture is universal, independent of microscopic details of
the coupling.Comment: 4 pages, 2 figures; acknowledgements and references adde
Fractional plateaus in the Coulomb blockade of coupled quantum dots
Ground-state properties of a double-large-dot sample connected to a reservoir
via a single-mode point contact are investigated. When the interdot
transmission is perfect and the dots controlled by the same dimensionless gate
voltage, we find that for any finite backscattering from the barrier between
the lead and the left dot, the average dot charge exhibits a Coulomb-staircase
behavior with steps of size e/2 and the capacitance peak period is halved. The
interdot electrostatic coupling here is weak. For strong tunneling between the
left dot and the lead, we report a conspicuous intermediate phase in which the
fractional plateaus get substantially altered by an increasing slope.Comment: 6 pages, 4 figures, final versio
Fano resonances and Aharonov-Bohm effects in transport through a square quantum dot molecule
We study the Aharonov-Bohm effect in a coupled 22 quantum dot array
with two-terminals. A striking conductance dip arising from the Fano
interference is found as the energy levels of the intermediate dots are
mismatched, which is lifted in the presence of a magnetic flux. A novel five
peak structure is observed in the conductance for large mismatch. The
Aharonov-Bohm evolution of the linear conductance strongly depends on the
configuration of dot levels and interdot and dot-lead coupling strengths. In
addition, the magnetic flux and asymmetry between dot-lead couplings can induce
the splitting and combination of the conductance peak(s).Comment: 15 pages, 7 figures, Revtex, to be published in Phys. Rev.
Localization of interacting electrons in quantum dot arrays driven by an ac-field
We investigate the dynamics of two interacting electrons moving in a
one-dimensional array of quantum dots under the influence of an ac-field. We
show that the system exhibits two distinct regimes of behavior, depending on
the ratio of the strength of the driving field to the inter-electron Coulomb
repulsion. When the ac-field dominates, an effect termed coherent destruction
of tunneling occurs at certain frequencies, in which transport along the array
is suppressed. In the other, weak-driving, regime we find the surprising result
that the two electrons can bind into a single composite particle -- despite the
strong Coulomb repulsion between them -- which can then be controlled by the
ac-field in an analogous way. We show how calculation of the Floquet
quasienergies of the system explains these results, and thus how ac-fields can
be used to control the localization of interacting electron systems.Comment: 7 pages, 6 eps figures V2. Minor changes, this version to be
published in Phys. Rev.
Coulomb correlations effects on localized charge relaxation in the coupled quantum dots
We analyzed localized charge time evolution in the system of two interacting
quantum dots (QD) (artificial molecule) coupled with the continuous spectrum
states. We demonstrated that Coulomb interaction modifies relaxation rates and
is responsible for non-monotonic time evolution of the localized charge. We
suggested new mechanism of this non-monotonic charge time evolution connected
with charge redistribution between different relaxation channels in each QD.Comment: 10 pages, 10 figure
Conductance and persistent current of a quantum ring coupled to a quantum wire under external fields
The electronic transport of a noninteracting quantum ring side-coupled to a
quantum wire is studied via a single-band tunneling tight-binding Hamiltonian.
We found that the system develops an oscillating band with antiresonances and
resonances arising from the hybridization of the quasibound levels of the ring
and the coupling to the quantum wire. The positions of the antiresonances
correspond exactly to the electronic spectrum of the isolated ring. Moreover,
for a uniform quantum ring the conductance and the persistent current density
were found to exhibit a particular odd-even parity related with the ring-order.
The effects of an in-plane electric field was also studied. This field shifts
the electronic spectrum and damps the amplitude of the persistent current
density. These features may be used to control externally the energy spectra
and the amplitude of the persistent current.Comment: Revised version, 7 pages and 9 figures. To appear in Phys. Rev.
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