642 research outputs found
Single-Electron Effects in a Coupled Dot-Ring System
Aharonov-Bohm oscillations are studied in the magnetoconductance of a
micron-sized open quantum ring coupled capacitively to a Coulomb-blockaded
quantum dot. As the plunger gate of the dot is modulated and tuned through a
conductance resonance, the amplitude of the Aharonov-Bohm oscillations in the
transconductance of the ring displays a minimum. We demonstrate that the effect
is due to a single-electron screening effect, rather than to dephasing.
Aharonov-Bohm oscillations in a quantum ring can thus be used for the detection
of single charges.Comment: 5 pages, 3 figure
Imaging the lateral shift of a quantum-point contact using scanning-gate microscopy
We perform scanning-gate microscopy on a quantum-point contact. It is defined
in a high-mobility two-dimensional electron gas of an AlGaAs/GaAs
heterostructure, giving rise to a weak disorder potential. The lever arm of the
scanning tip is significantly smaller than that of the split gates defining the
conducting channel of the quantum-point contact. We are able to observe that
the conducting channel is shifted in real space when asymmetric gate voltages
are applied. The observed shifts are consistent with transport data and
numerical estimations.Comment: 5 pages, 3 figure
Singlet-Triplet Transition Tuned by Asymmetric Gate Voltages in a Quantum Ring
Wavefunction and interaction effects in the addition spectrum of a Coulomb
blockaded many electron quantum ring are investigated as a function of
asymmetrically applied gate voltages and magnetic field. Hartree and exchange
contributions to the interaction are quantitatively evaluated at a crossing
between states extended around the ring and states which are more localized in
one arm of the ring. A gate tunable singlet-triplet transition of the two
uppermost levels of this many electron ring is identified at zero magnetic
field.Comment: 4 page
Kondo Effect in a Many-Electron Quantum Ring
The Kondo effect is investigated in a many-electron quantum ring as a
function of magnetic field. For fields applied perpendicular to the plane of
the ring a modulation of the Kondo effect with the Aharonov-Bohm period is
observed. This effect is discussed in terms of the energy spectrum of the ring
and the parametrically changing tunnel coupling. In addition, we use gate
voltages to modify the ground-state spin of the ring. The observed splitting of
the Kondo-related zero-bias anomaly in this configuration is tuned with an
in-plane magnetic field.Comment: 4 pages, 4 figure
A low-temperature dynamic mode scanning force microscope operating in high magnetic fields
A scanning force microscope was implemented operating at temperatures below
4.2K and in magnetic fields up to 8T. Piezoelectric quartz tuning forks were
employed for non optical tip-sample distance control in the dynamic operation
mode. Fast response was achieved by using a phase-locked loop for driving the
mechanical oscillator. Possible applications of this setup for various scanning
probe techniques are discussed.Comment: 5 pages, 5 figures, submitted to "Review of Scientific Instruments
- …