148 research outputs found
Single hole transistor in a p-Si/SiGe quantum well
A single hole transistor is patterned in a p-Si/SiGe quantum well by applying
voltages to nanostructured top gate electrodes. Gating is achieved by oxidizing
the etched semiconductor surface and the mesa walls before evaporation of the
top gates. Pronounced Coulomb blockade effects are observed at small coupling
of the transistor island to source and drain.Comment: 3 pages, 3 figure
Optimized stray-field-induced enhancement of the electron spin precession by buried Fe gates
The magnetic stray field from Fe gates is used to modify the spin precession
frequency of InGaAs/GaAs quantum-well electrons in an external magnetic field.
By using an etching process to position the gates directly in the plane of the
quantum well, the stray-field influence on the spin precession increases
significantly compared with results from previous studies with top-gated
structures. In line with numerical simulations, the stray-field-induced
precession frequency increases as the gap between the ferromagnetic gates is
reduced. The inhomogeneous stray field leads to additional spin dephasing.Comment: 4 pages, 2 figure
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
Nonthermal Emission from Accreting and Merging Clusters of Galaxies
We compare the nonthermal emission from clusters of galaxies undergoing minor
mergers (``accreting'' clusters) and major mergers (``merging'' clusters). For
accreting clusters, the radial distribution of the nonthermal emission in the
clusters is also calculated. The relativistic electrons, which are the origin
of the nonthermal radiation through inverse Compton (IC) and synchrotron
mission, are assumed to be accelerated at shocks produced by accretion or
mergers. We estimate the typical accretion rate and merger probability
according to a hierarchical clustering model. We show that the total luminosity
of IC emission from accreting and merging clusters are similar. On the other
hand, the luminosity of synchrotron radio emission of the former is much
smaller than that of the latter. We show that about 10% of clusters at z~0
should have hard X-ray and radio nonthermal emissions due to their last major
merger, which are comparable to or dominate those due to ongoing accretion.
Moreover, 20-40% of clusters should have significant EUV emission due to their
last merger. We also investigate the case where the criterion of mergers is
relaxed. If we extend the definition of a merger to an increase in the mass of
the larger subcluster by at least 10% of its initial mass, about 20-30% of
clusters at z~0 should have hard X-ray and radio nonthermal emissions due to
the merger even in a low density universe. We compare the results with
observations. We find that the observed EUV emission from clusters is not
attributed to accretion. If the diffuse radio emission observed in clusters is
synchrotron emission from electrons accelerated via accretion or merging, the
magnetic fields of clusters are generally as small as ~0.1 mu G.Comment: 33 pages, 18 figures, accepted by Ap
Fano effect in a ring-dot system with tunable coupling
Transport measurements are presented on a quantum ring that is tunnel-coupled
to a quantum dot. When the dot is in the Coulomb blockade regime, but strongly
coupled to the open ring, Fano line shapes are observed in the current through
the ring, when the electron number in the dot changes by one. The symmetry of
the Fano resonances is found to depend on the magnetic flux penetrating the
area of the ring and on the strength of the ring-dot coupling. At temperatures
above T=0.65 K the Fano effect disappears while the Aharonov-Bohm interference
in the ring persists up to T=4.2 K. Good agreement is found between these
experimental observations and a single channel scattering matrix model
including decoherence in the dot.Comment: 9 pages, 6 figure
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