371 research outputs found
Cotunneling drag effect in Coulomb-coupled quantum dots
In Coulomb drag, a current flowing in one conductor can induce a voltage
across an adjacent conductor via the Coulomb interaction. The mechanisms
yielding drag effects are not always understood, even though drag effects are
sufficiently general to be seen in many low-dimensional systems. In this
Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot
(CC-DQD) and, through both experimental and theoretical arguments, identify
cotunneling as essential to obtaining a correct qualitative understanding of
the drag behavior.Comment: Main text: 5 pages, 5 figures; SM: 11 pages, 5 figures, 1 tabl
Probabilistic Fragmentation and Effective Power Law
A simple fragmentation model is introduced and analysed. We show that, under
very general conditions, an effective power law for the mass distribution
arises with realistic exponent. This exponent has a universal limit, but in
practice the effective exponent depends on the detailed breaking mechanism and
the initial conditions. This dependence is in good agreement with experimental
results of fragmentation.Comment: 4 pages Revtex, 2 figures, zipped and uuencode
Pseudospin-Resolved Transport Spectroscopy of the Kondo Effect in a Double Quantum Dot
We report measurements of the Kondo effect in a double quantum dot (DQD),
where the orbital states act as pseudospin states whose degeneracy contributes
to Kondo screening. Standard transport spectroscopy as a function of the bias
voltage on both dots shows a zero-bias peak in conductance, analogous to that
observed for spin Kondo in single dots. Breaking the orbital degeneracy splits
the Kondo resonance in the tunneling density of states above and below the
Fermi energy of the leads, with the resonances having different pseudospin
character. Using pseudospin-resolved spectroscopy, we demonstrate the
pseudospin character by observing a Kondo peak at only one sign of the bias
voltage. We show that even when the pseudospin states have very different
tunnel rates to the leads, a Kondo temperature can be consistently defined for
the DQD system.Comment: Text and supplementary information. Text: 4 pages, 5 figures.
Supplementary information: 4 pages, 4 figure
Singlet-triplet transition in a single-electron transistor at zero magnetic field
We report sharp peaks in the differential conductance of a single-electron
transistor (SET) at low temperature, for gate voltages at which charge
fluctuations are suppressed. For odd numbers of electrons we observe the
expected Kondo peak at zero bias. For even numbers of electrons we generally
observe Kondo-like features corresponding to excited states. For the latter,
the excitation energy often decreases with gate voltage until a new zero-bias
Kondo peak results. We ascribe this behavior to a singlet-triplet transition in
zero magnetic field driven by the change of shape of the potential that
confines the electrons in the SET.Comment: 4 p., 4 fig., 5 new ref. Rewrote 1st paragr. on p. 4. Revised author
list. More detailed fit results on page 3. A plotting error in the horizontal
axis of Fig. 1b and 3 was corrected, and so were the numbers in the text read
from those fig. Fig. 4 was modified with a better temperature calibration
(changes are a few percent). The inset of this fig. was removed as it is
unnecessary here. Added remarks in the conclusion. Typos are correcte
Novel Properties of The Apparent Metal-Insulator Transition in Two-Dimensional Systems
The low-temperature conductivity of low-density, high-mobility,
two-dimensional hole systems in GaAs was studied. We explicitly show that the
metal-insulator transition, observed in these systems, is characterized by a
well-defined critical density, p_0c. We also observe that the low-temperature
conductivity of these systems depends linearly on the hole density, over a wide
density range. The high-density linear conductivity extrapolates to zero at a
density close to the critical density.Comment: 4 Figure
Observation of the Metal-Insulator Transition in Two-Dimensional n-type GaAs
The observation of a carrier-density driven metal-insulator transition in
n-type GaAs-based heterostructure is reported. Although weaker than in
comparable-quality p-type GaAs samples, the main features of the transition are
rather similar.Comment: 3 pages, 3 figure
From the Kondo Regime to the Mixed-Valence Regime in a Single-Electron Transistor
We demonstrate that the conductance through a single-electron transistor at
low temperature is in quantitative agreement with predictions of the
equilibrium Anderson model. When an unpaired electron is localized within the
transistor, the Kondo effect is observed. Tuning the unpaired electron's energy
toward the Fermi level in nearby leads produces a cross-over between the Kondo
and mixed-valence regimes of the Anderson model.Comment: 3 pages plus one 2 page postscript file of 5 figures. Submitted to
PR
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