196 research outputs found
Non adiabatic features of electron pumping through a quantum dot in the Kondo regime
We investigate the behavior of the dc electronic current, Jdc, in an
interacting quantum dot driven by two ac local potentials oscillating with a
frequency, Omega0, and a phase-lag, phi. We provide analytical functions to
describe the fingerprints of the Coulomb interaction in an experimental Jdc vs
phi characteristic curve. We show that the Kondo resonance reduces at low
temperatures the frequency range for the linear behavior of Jdc in Omega0 to
take place and determines the evolution of the dc-current as the temperature
increases.Comment: 8 pages, 7 figure
Interpolative method for transport properties of quantum dots in the Kondo regime
We present an interpolative method for describing coherent transport through
an interacting quantum dot. The idea of the method is to construct an
approximate electron self-energy which becomes exact both in the limits of weak
and strong coupling to the leads. The validity of the approximation is first
checked for the case of a single (spin-degenerate) dot level. A generalization
to the multilevel case is then discussed. We present results both for the
density of states and the temperature dependent linear conductance showing the
transition from the Kondo to the Coulomb blockade regime.Comment: 8 pages, 3 figures, includes lamuphys.sty, submitted to the
Proceedings of the XVI Sitges Conference on Statistical Mechanic
Local density of states on a vibrational quantum dot out of equilibrium
We calculate the nonequilibrium local density of states on a vibrational
quantum dot coupled to two electrodes at T=0 using a numerically exact
diagrammatic Monte Carlo method. Our focus is on the interplay between the
electron-phonon interaction strength and the bias voltage. We find that the
spectral density exhibits a significant voltage dependence if the voltage
window includes one or more phonon sidebands. A comparison with
well-established approximate approaches indicates that this effect could be
attributed to the nonequilibrium distribution of the phonons. Moreover, we
discuss the long transient dynamics caused by the electron-phonon coupling.Comment: 9 pages, 11 figure
General transport properties of superconducting quantum point contacts: a Green functions approach
We discuss the general transport properties of superconducting quantum point
contacts. We show how these properties can be obtained from a microscopic model
using nonequilibrium Green function techniques. For the case of a one-channel
contact we analyze the response under different biasing conditions: constant
applied voltage, current bias and microwave-induced transport. Current
fluctuations are also analyzed with particular emphasis on thermal and
shot-noise. Finally, the case of superconducting transport through a resonant
level is discussed. The calculated properties show a remarkable agreement with
the available experimental data from atomic-size contacts measurements. We
suggest the possibility of extending this comparison to several other
predictions of the theory.Comment: 10 pages, revtex, 8 figures, submitted to a special issue of
Superlattices and Microstructure
Influence of spin filtering and spin mixing on the subgap structure of I-V characteristics in superconducting quantum point contact
The effect of spin filtering and spin mixing on the dc electric current for
voltage biased magnetic quantum point contact with superconducting leads is
theoretically studied. The I-V characteristics are calculated for the whole
range of spin filtering and spin mixing parameters. It is found that with
increasing of spin filtering the subharmonic step structure of the dc electric
current, typical for low-transparency junction and junction without
considerable spin filtering qualitatively changes. In the lower voltage region
and for small enough spin mixing the peak structure arises. When spin mixing
increases the peak subgap structure evolves to the step structure. The voltages
where subharmonic gap features are located are found to be sensitive to the
value of spin filtering. The positions of peaks and steps are calculated
analytically and the evolution of the subgap structure from well-known tunnel
limit to the large spin filtering case is explained in terms of multiple
Andreev reflection (MAR) processes. In particular, it is found that for large
spin filtering the subgap feature at arises from and
order MAR processes, while in the tunnel limit the step at
is known to result from order MAR process.Comment: 9 pages, 3 figure
Long transient dynamics in the Anderson-Holstein model out of equilibrium
We calculate the time dependent nonequilibrium current through a single level
quantum dot strongly coupled to a vibrational mode. The nonequilibrium real
time dynamics caused by an instantaneous coupling of the leads to the quantum
dot is discussed using an approximate method. The approach, which is specially
designed for the strong polaronic regime, is based on the so-called polaron
tunneling approximation. Considering different initial dot occupations, we show
that a common steady state is reached after times much larger than the typical
electron tunneling times due to a polaron blocking effect in the dot charge. A
direct comparison is made with numerically exact data, showing good agreement
for the time scales accessible by the diagrammatic Monte Carlo simulation
method
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