3,010 research outputs found
Time-Resolved Detection of Individual Electrons in a Quantum Dot
We present measurements on a quantum dot and a nearby, capacitively coupled,
quantum point contact used as a charge detector. With the dot being weakly
coupled to only a single reservoir, the transfer of individual electrons onto
and off the dot can be observed in real time in the current signal from the
quantum point contact. From these time-dependent traces, the quantum mechanical
coupling between dot and reservoir can be extracted quantitatively. A similar
analysis allows the determination of the occupation probability of the dot
states.Comment: 3 pages, 3 figure
Finite bias charge detection in a quantum dot
We present finite bias measurements on a quantum dot coupled capacitively to
a quantum point contact used as a charge detector. The transconductance signal
measured in the quantum point contact at finite dot bias shows structure which
allows us to determine the time-averaged charge on the dot in the non-blockaded
regime and to estimate the coupling of the dot to the leads.Comment: 6 pages, 4 figure
In Situ Treatment of a Scanning Gate Microscopy Tip
In scanning gate microscopy, where the tip of a scanning force microscope is
used as a movable gate to study electronic transport in nanostructures, the
shape and magnitude of the tip-induced potential are important for the
resolution and interpretation of the measurements. Contaminations picked up
during topography scans may significantly alter this potential. We present an
in situ high-field treatment of the tip that improves the tip-induced
potential. A quantum dot was used to measure the tip-induced potential.Comment: 3 pages, 1 figure, minor changes to fit published versio
Imaging a Coupled Quantum Dot - Quantum Point Contact System
We performed measurements on a quantum dot and a capacitively coupled quantum
point contact by using the sharp metallic tip of a low-temperature scanning
force microscope as a scanned gate. The quantum point contact served as a
detector for charges on the dot or nearby. It allowed us to distinguish single
electron charging events in several charge traps from charging events on the
dot. We analyzed the tip-induced potential quantitatively and found its shape
to be independent of the voltage applied to the tip within a certain range of
parameters. We estimate that the trap density is below 0.1% of the doping
density and that the interaction energy between the quantum dot and a trap is a
significant portion of the dot's charging energy. Possibly, such charge traps
are the reason for frequently observed parametric charge rearrangements.Comment: 6 pages, 5 figure
Two-subband quantum Hall effect in parabolic quantum wells
The low-temperature magnetoresistance of parabolic quantum wells displays
pronounced minima between integer filling factors. Concomitantly the Hall
effect exhibits overshoots and plateau-like features next to well-defined
ordinary quantum Hall plateaus. These effects set in with the occupation of the
second subband. We discuss our observations in the context of single-particle
Landau fan charts of a two-subband system empirically extended by a density
dependent subband separation and an enhanced spin-splitting g*.Comment: 5 pages, submitte
Measurement of the Tip-Induced Potential in Scanning Gate Experiments
We present a detailed experimental study on the electrostatic interaction
between a quantum dot and the metallic tip of a scanning force microscope. Our
method allowed us to quantitatively map the tip-induced potential and to
determine the spatial dependence of the tip's lever arm with high resolution.
We find that two parts of the tip-induced potential can be distinguished, one
that depends on the voltage applied to the tip and one that is independent of
this voltage. The first part is due to the metallic tip while we interpret the
second part as the effect of a charged dielectric particle on the tip. In the
measurements of the lever arm we find fine structure that depends on which
quantum state we study. The results are discussed in view of scanning gate
experiments where the tip is used as a movable gate to study nanostructures.Comment: 7 pages, 5 figures, minor changes to fit published versio
Cotunneling-mediated transport through excited states in the Coulomb blockade regime
We present finite bias transport measurements on a few-electron quantum dot.
In the Coulomb blockade regime, strong signatures of inelastic cotunneling
occur which can directly be assigned to excited states observed in the
non-blockaded regime. In addition, we observe structures related to sequential
tunneling through the dot, occuring after it has been excited by an inelastic
cotunneling process. We explain our findings using transport calculations
within the real-time Green's function approach, including diagrams up to fourth
order in the tunneling matrix elements.Comment: 4 pages, 3 figure
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