1,469 research outputs found
Electron Mobility and Magneto Transport Study of Ultra-Thin Channel Double-Gate Si MOSFETs
We report on detailed room temperature and low temperature transport
properties of double-gate Si MOSFETs with the Si well thickness in the range
7-17 nm. The devices were fabricated on silicon-on-insulator wafers utilizing
wafer bonding, which enabled us to use heavily doped metallic back gate. We
observe mobility enhancement effects at symmetric gate bias at room
temperature, which is the finger print of the volume inversion/accumulation
effect. An asymmetry in the mobility is detected at 300 K and at 1.6 K between
the top and back interfaces of the Si well, which is interpreted to arise from
different surface roughnesses of the interfaces. Low temperature peak
mobilities of the reported devices scale monotonically with Si well thickness
and the maximum low temperature mobility was 1.9 m2/Vs, which was measured from
a 16.5 nm thick device. In the magneto transport data we observe single and two
sub-band Landau level filling factor behavior depending on the well thickness
and gate biasing
Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots
By means of sequential and cotunneling spectroscopy, we study the tunnel
couplings between metallic leads and individual levels in a carbon nanotube
quantum dot. The levels are ordered in shells consisting of two doublets with
strong- and weak-tunnel couplings, leading to gate-dependent level
renormalization. By comparison to a one- and two-shell model, this is shown to
be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a
parallel magnetic field is shown to reduce this mixing and thus suppress the
effects of tunnel renormalization.Comment: 5 pages, 3 figures; revised version as publishe
Coulomb Drag as a Probe of the Nature of Compressible States in a Magnetic Field
Magneto-drag reveals the nature of compressible states and the underlying
interplay of disorder and interactions. At \nu=3/2 a clear T^{4/3} dependence
is observed, which signifies the metallic nature of the N=0 Landau level. In
contrast, drag in higher Landau levels reveals an additional contribution,
which anomalously grows with decreasing T before turning to zero following a
thermal activation law. The anomalous drag is discussed in terms of
electron-hole asymmetry arising from disorder and localization, and the
crossover to normal drag at high fields as due to screening of disorder.Comment: 5 pages, 4 figure
Exciton condensate at a total filling factor of 1 in Corbino 2D electron bilayers
Magneto-transport and drag measurements on a quasi-Corbino 2D electron
bilayer at the systems total filling factor 1 (v_tot=1) reveal a drag voltage
that is equal in magnitude to the drive voltage as soon as the two layers begin
to form the expected v_tot=1 exciton condensate. The identity of both voltages
remains present even at elevated temperatures of 0.25 K. The conductance in the
current carrying layer vanishes only in the limit of strong coupling between
the two layers and at T->0 K which suggests the presence of an excitonic
circular current
A test of the Feynman scaling in the fragmentation region
The result of the direct measurement of the fragmentation region will be presented. The result will be obtained at the CERN proton-antiproton collider, being exposured the Silicon calorimeters inside beam pipe. This experiment clarifies a long riddle of cosmic ray physics, whether the Feynman scaling does villate at the fragmentation region or the Iron component is increasing at 10 to the 15th power eV
Solar Neutron Events of October-November 2003
During the period when the Sun was intensely active on October-November 2003,
two remarkable solar neutron events were observed by the ground-based neutron
monitors. On October 28, 2003, in association with an X17.2 large flare, solar
neutrons were detected with high statistical significance (6.4 sigma) by the
neutron monitor at Tsumeb, Namibia. On November 4, 2003, in association with an
X28 class flare, relativistic solar neutrons were observed by the neutron
monitors at Haleakala in Hawaii and Mexico City, and by the solar neutron
telescope at Mauna Kea in Hawaii simultaneously. Clear excesses were observed
at the same time by these detectors, with the significance calculated as 7.5
sigma for Haleakala, and 5.2 sigma for Mexico City. The detector onboard the
INTEGRAL satellite observed a high flux of hard X-rays and gamma-rays at the
same time in these events. By using the time profiles of the gamma-ray lines,
we can explain the time profile of the neutron monitor. It appears that
neutrons were produced at the same time as the gamma-ray emission.Comment: 35 pages, 21 figures, accepted for publication in Ap
Local implicit modeling of blood vessels for interactive simulation
International audienceIn the context of computer-based simulation, contact management requires an accurate, smooth, but still efficient surface model for the blood vessels. A new implicit model is proposed, consisting of a tree of local implicit surfaces generated by skeletons ({\em blobby models}). The surface is reconstructed from data points by minimizing an energy, alternating with an original blob selection and subdivision scheme. The reconstructed models are very efficient for simulation and were shown to provide a sub-voxel approximation of the vessel surface on 5 patients
Collapse of ringlike structures in 2DEGs under tilted magnetic fields
In the quantum Hall regime, the longitudinal resistivity plotted
as a density--magnetic-field () diagram displays ringlike structures
due to the crossings of two sets of spin split Landau levels from different
subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801
(2005)]. For tilted magnetic fields, some of these ringlike structures "shrink"
as the tilt angle is increased and fully collapse at . Here we theoretically investigate the topology of these structures
via a non-interacting model for the 2DEG. We account for the inter Landau-level
coupling induced by the tilted magnetic field via perturbation theory. This
coupling results in anti-crossings of Landau levels with parallel spins. With
the new energy spectrum, we calculate the corresponding diagram of
the density of states (DOS) near the Fermi level. We argue that the DOS
displays the same topology as in the diagram. For the
ring with filling factor , we find that the anti-crossings make it
shrink for increasing tilt angles and collapse at a large enough angle. Using
effective parameters to fit the data, we find a collapsing
angle . Despite this factor-of-two discrepancy with
the experimental data, our model captures the essential mechanism underlying
the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in
August 2008 in Foz do Igua\c{c}u, Brazi
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