2,986 research outputs found
Nongalvanic thermometry for ultracold two-dimensional electron domains
Measuring the temperature of a two-dimensional electron gas at temperatures
of a few mK is a challenging issue, which standard thermometry schemes may fail
to tackle. We propose and analyze a nongalvanic thermometer, based on a quantum
point contact and quantum dot, which delivers virtually no power to the
electron system to be measured.Comment: 5 pages, 3 figure
Single-electron tunneling in InP nanowires
We report on the fabrication and electrical characterization of field-effect
devices based on wire-shaped InP crystals grown from Au catalyst particles by a
vapor-liquid-solid process. Our InP wires are n-type doped with diameters in
the 40-55 nm range and lengths of several microns. After being deposited on an
oxidized Si substrate, wires are contacted individually via e-beam fabricated
Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor
temperature dependence. The distance between the electrodes varies between 0.2
and 2 micron. The electron density in the wires is changed with a back gate.
Low-temperature transport measurements show Coulomb-blockade behavior with
single-electron charging energies of ~1 meV. We also demonstrate energy
quantization resulting from the confinement in the wire.Comment: 4 pages, 3 figure
The Kondo Effect in the Unitary Limit
We observe a strong Kondo effect in a semiconductor quantum dot when a small
magnetic field is applied. The Coulomb blockade for electron tunneling is
overcome completely by the Kondo effect and the conductance reaches the
unitary-limit value. We compare the experimental Kondo temperature with the
theoretical predictions for the spin-1/2 Anderson impurity model. Excellent
agreement is found throughout the Kondo regime. Phase coherence is preserved
when a Kondo quantum dot is included in one of the arms of an Aharonov-Bohm
ring structure and the phase behavior differs from previous results on a
non-Kondo dot.Comment: 10 page
Electronic Transport Spectroscopy of Carbon Nanotubes in a Magnetic Field
We report magnetic field spectroscopy measurements in carbon nanotube quantum
dots exhibiting four-fold shell structure in the energy level spectrum. The
magnetic field induces a large splitting between the two orbital states of each
shell, demonstrating their opposite magnetic moment and determining transitions
in the spin and orbital configuration of the quantum dot ground state. We use
inelastic cotunneling spectroscopy to accurately resolve the spin and orbital
contributions to the magnetic moment. A small coupling is found between
orbitals with opposite magnetic moment leading to anticrossing behavior at zero
field.Comment: 7 pages, 4 figure
Development of a measurement platformon a light airplane and analysis of airborne measurementsin the atmospheric boundary layer
In the present paper we provide an overview of a long term research project aimed at setting up a suitable platform
for measurements in the atmospheric boundary layer on a light airplane along with some preliminary results
obtained from fi eld campaigns at selected sites. Measurements of air pressure, temperature and relative humidity
have been performed in various Alpine valleys up to a height of about 2500 m a.m.s.l. By means of GPS resources
and specifi c post-processing procedures careful positioning of measurement points within the explored domain
has been achieved. The analysis of collected data allowed detailed investigation of atmospheric vertical structures
and dynamics typical of valley environment, such as morning transition from ground based inversion to fully
developed well mixed convective boundary layer. Based on data collected along fl ights, 3D fi elds of the explored
variables have been detected and identifi ed through application of geostatistical techniques (Kriging). The adopted
procedures allowed evaluation of the intrinsic statistical structure of the spatial distribution of measured quantities
and the estimate of the values of the same variable at unexplored locations by suitable weighted average of data
recorded at close locations. Results thus obtained are presented and discussed
Magnetically induced chessboard pattern in the conductance of a Kondo quantum dot
We quantitatively describe the main features of the magnetically induced
conductance modulation of a Kondo quantum dot -- or chessboard pattern -- in
terms of a constant-interaction double quantum dot model. We show that the
analogy with a double dot holds down to remarkably low magnetic fields. The
analysis is extended by full 3D spin density functional calculations.
Introducing an effective Kondo coupling parameter, the chessboard pattern is
self-consistently computed as a function of magnetic field and electron number,
which enables us to quantitatively explain our experimental data.Comment: 4 pages, 3 color figure
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