2,570 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
Phase coherence in the inelastic cotunneling regime
Two quantum dots with tunable mutual tunnel coupling have been embedded in a
two-terminal Aharonov-Bohm geometry. Aharonov-Bohm oscillations are
investigated in the cotunneling regime. Visibilities of more than 0.8 are
measured indicating that phase-coherent processes are involved in the elastic
and inelastic cotunneling. An oscillation-phase change of pi is detected as a
function of bias voltage at the inelastic cotunneling onset.Comment: 4 pages, 4 figure
Full electrical control of Charge and Spin conductance through Interferometry of Edge States in Topological Insulators
We investigate electron interferometry of edge states in Topological
Insulators. We show that, when inter-boundary coupling is induced at two
quantum point contacts of a four terminal setup, both Fabry-P\'erot-like and
Aharonov-Bohm-like loop processes arise. These underlying interference effects
lead to a full electrically controllable system, where the magnitude of charge
and spin linear conductances can be tuned by gate voltages, without applying
magnetic fields. In particular we find that, under appropriate conditions,
inter-boundary coupling can lead to negative values of the conductance.
Furthermore, the setup also allows to selectively generate pure charge or pure
spin currents, by choosing the voltage bias configuration.Comment: 12 pages, 5 figures (expanded discussion section, corrected typos
Aharonov-Bohm oscillations in the presence of strong spin-orbit interactions
We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring
structure defined by local anodic oxidation on a p-type GaAs heterostructure
with strong spin-orbit interactions. Clear beating patterns observed in the raw
data can be interpreted in terms of a spin geometric phase. Besides h/e
oscillations, we resolve the contributions from the second harmonic of AB
oscillations and also find a beating in these h/2e oscillations. A resistance
minimum at B=0T, present in all gate configurations, is the signature of
destructive interference of the spins propagating along time-reversed paths.Comment: 4 pages, 3 figures, published versio
U.S.-CANADA BORDER DISPUTES IN GRAINS: DYNAMIC INTERFACE BETWEEN THE FREE TRADE AGREEMENT AND TRADE REMEDY LAWS
Agricultural trade between the United States and Canada has been contentious since the inception of the CUSTA agreement in 1989. Even though Canadian exports of wheat and barley are not found to have violated U.S. trade remedy laws, friction seems likely to continue as long as the surge in Canadian exports remains unabated. Gradual harmonization of trade policies, farm subsidy programs, and marketing institutions may reduce trade disputes between the two countries in the future. To diffuse the threat of future trade disputes, a Canada - U.S. joint research team should be formed to deal with the matter through better understanding for causes of the disputes.bilateral trade, free trade agreement, trade disputes, trade remedy laws, farm income, farm price, harmonization, International Relations/Trade,
Spin Effects in a Quantum Ring
Recent experiments are reviewed that explore the spin states of a ring-shaped
many-electron quantum dot. Coulomb-blockade spectroscopy is used to access the
spin degree of freedom. The Zeeman effect observed for states with successive
electron number allows to select possible sequences of spin ground states of
the ring. Spin-paired orbital levels can be identified by probing their
response to magnetic fields normal to the plane of the ring and electric fields
caused by suitable gate voltages. This narrows down the choice of ground-state
spin sequences. A gate-controlled singlet--triplet transition is identified and
the size of the exchange interaction matrix element is determined.Comment: 13 pages, 3 figures, Proceedings of the QD2004 conference in Banf
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