630 research outputs found
Thermopower in the Coulomb blockade regime for Laughlin quantum dots
Using the conformal field theory partition function of a Coulomb-blockaded
quantum dot, constructed by two quantum point contacts in a Laughlin quantum
Hall bar, we derive the finite-temperature thermodynamic expression for the
thermopower in the linear-response regime. The low-temperature results for the
thermopower are compared to those for the conductance and their capability to
reveal the structure of the single-electron spectrum in the quantum dot is
analyzed.Comment: 11 pages, 3 figures, Proceedings of the 10-th International Workshop
"Lie Theory and Its Applications in Physics", 17-23 June 2013, Varna,
Bulgari
Adiabatic pumping in the mixed-valence and Kondo regimes
We investigate adiabatic pumping through a quantum dot with a single level in
the mixed-valence and Kondo regimes using the slave-boson mean field
approximation. The pumped current is driven by a gauge potential due to
time-dependent tunneling barriers as well as by the modulation of the Friedel
phase. The sign of the former contribution depends on the strength of the
Coulomb interaction. Under finite magnetic fields, the separation of the spin
and charge currents peculiar to the Kondo effect occurs.Comment: RevTeX, 4+pages, 4 figures, textual improvemen
SU(4) and SU(2) Kondo Effects in Carbon Nanotube Quantum Dots
We study the SU(4) Kondo effect in carbon nanotube quantum dots, where doubly
degenerate orbitals form 4-electron ``shells''. The SU(4) Kondo behavior is
investigated for one, two and three electrons in the topmost shell. While the
Kondo state of two electrons is quenched by magnetic field, in case of an odd
number of electrons two types of SU(2) Kondo effect may survive. Namely, the
spin SU(2) state is realized in the magnetic field parallel to the nanotube
(inducing primarily orbital splitting). Application of the perpendicular field
(inducing Zeeman splitting) results in the orbital SU(2) Kondo effect.Comment: 5 pages. Some material was previously posted in cond-mat/0608573, v
Electronic properties of quantum dots formed by magnetic double barriers in quantum wires
The transport through a quantum wire exposed to two magnetic spikes in series
is modeled. We demonstrate that quantum dots can be formed this way which
couple to the leads via magnetic barriers. Conceptually, all quantum dot states
are accessible by transport experiments. The simulations show Breit-Wigner
resonances in the closed regime, while Fano resonances appear as soon as one
open transmission channel is present. The system allows to tune the dot's
confinement potential from sub-parabolic to superparabolic by experimentally
accessible parameters.Comment: 5 pages, 5 figure
Planar nanocontacts with atomically controlled separation
We have developed a technology to reproducibly make gaps with distance
control on the single atom scale. The gold contacts are flat on the nanometre
scale and are fabricated on an oxidized aluminium film that serves as a gate.
We show that these contacts are clean and can be stabilized via chemical
functionalization. Deposition of conjugated molecules leads to an increase in
the gap conductance of several orders of magnitude. Stable current-voltage
characteristics at room temperature are slightly nonlinear. At low temperature,
they are highly nonlinear and show a clear gate effect.Comment: 4 pages, 3 figure
Transport through a double quantum dot in the sequential- and co- tunneling regimes
We study transport through a double quantum dot, both in the sequential
tunneling and cotunneling regimes. Using a master equation approach, we find
that, in the sequential tunneling regime, the differential conductance
as a function of the bias voltage has a number of satellite
peaks with respect to the main peak of the Coulomb blockade diamond. The
position of these peaks is related to the interdot tunnel splitting and the
singlet-triplet splitting. We find satellite peaks with both {\em positive} and
{\em negative} values of differential conductance for realistic parameter
regimes. Relating our theory to a microscopic (Hund-Mulliken) model for the
double dot, we find a temperature regime for which the Hubbard ratio (=tunnel
coupling over on-site Coulomb repulsion) can be extracted from
in the cotunneling regime. In addition, we consider a combined effect of
cotunneling and sequential tunneling, which leads to new peaks (dips) in
inside the Coulomb blockade diamond below some temperature
scales, which we specify.Comment: 16 pages, 10 figure
Adiabatic charge pumping in almost open dots
We consider adiabatic charge transport through an almost open quantum dot. We
show that the charge transmitted in one cycle is quantized in the limit of
vanishing temperature and one-electron mean level spacing in the dot. The
explicit analytic expression for the pumped charge at finite temperature is
obtained for spinless electrons. The pumped charge is produced by both
non-dissipative and dissipative currents. The latter are responsible for the
corrections to charge quantization which are expressed through the conductance
of the system.Comment: 5 pages, 1 figur
Coherent probing of excited quantum dot states in an interferometer
Measurements of elastic and inelastic cotunneling currents are presented on a
two-terminal Aharonov--Bohm interferometer with a Coulomb blockaded quantum dot
embedded in each arm. Coherent current contributions, even in magnetic field,
are found in the nonlinear regime of inelastic cotunneling at finite bias
voltage. The phase of the Aharonov--Bohm oscillations in the current exhibits
phase jumps of at the onsets of inelastic processes. We suggest that
additional coherent elastic processes occur via the excited state. Our
measurement technique allows the detection of such processes on a background of
other inelastic current contributions and contains information about the
excited state occupation probability and the inelastic relaxation rates
- …