2,292 research outputs found
In-plane Magnetic Field Dependent Magnetoresistance of Gated Asymmetric Double Quantum Wells
We have investigated experimentally the magnetoresistance of strongly
asymmetric double-wells. The structures were prepared by inserting a thin
AlGaAs barrier into the GaAs buffer layer of a standard
modulation-doped GaAs/AlGaAs heterostructure. The resulting
double-well system consists of a nearly rectangular well and of a triangular
well coupled by tunneling through the thin barrier. With a proper choice of the
barrier parameters one can control the occupancy of the two wells and of the
two lowest (bonding and antibonding) subbands. The electron properties can be
further influenced by applying front- or back-gate voltage.Comment: 4 pages, 5 figures, elsart/PHYEAUTH macros; to be presented on the
EP2DS-15 Conference in Nara, Japan. Revised version. To appear in Physica
Novel critical field in magneto-resistance oscillation of 2DEG in asymmetric GaAs/AlGaAs double wells measured as a function of the in-plane magnetic field
We have investigated the magnetoresistance of strongly asymmetric double-well
structures formed by a thin AlGaAs barrier grown far from the interface in the
GaAs buffer of standard heterostructures. In magnetic fields oriented parallel
to the electron layers, the magnetoresistance exhibits an oscillation
associated with the depopulation of the higher occupied subband and with the
field-induced transition into a decoupled bilayer. In addition, the increasing
field transfers electrons from the triangular to rectangular well and, at high
enough field value, the triangular well is emptied. Consequently, the
electronic system becomes a single layer which leads to a sharp step in the
density of electron states and to an additional minimum in the
magnetoresistance curve.Comment: 3 pages, 3 figure
Electron magnetotransport in GaAs/AlGaAs superlattices with weak and strong inter-well coupling
We report on magnetotransport measurements in two MBE-grown GaAs/AlGaAs
superlattices formed by wide and narrow quantum wells and thin Si-doped
barriers subject to tilted magnetic fields. It has been shown that illumination
of the strongly coupled superlattice with narrow wells leads to reduction of
its dimensionality from the 3D to 2D. The illumination-induced transition is
revealed by remarkable change of magnetoresistance curves as compared to those
measured before illumination. The experimental data along with tight-binding
model calculations indicate that the illumination not only enhances the
electron concentration but also suppresses the electron tunneling through the
barriers.Comment: 3 pages, 3 figures, elsart/PHYEAUTH macros; presented on the LDSD
2007 Conference in the Caribbean Archipelago San Andres, Colombia. To be
published as a special issue of Microelectronics Journal (Elsevier
Magnetoresistance oscillations in GaAs/AlGaAs superlattices subject to in-plane magnetic fields
The MBE-grown GaAs/AlGaAs superlattice with Si-doped barriers has been used
to study a 3D-2D transition under the influence of the in-plane component of
applied magnetic field. The longitudinal magnetoresistance data measured in
tilted magnetic fields have been interpreted in terms of a simple tight-binding
model. The data provide values of basic parameters of the model and make it
possible to reconstruct the superlattice Fermi surface and to calculate the
density of states for the lowest Landau subbands. Positions of van Hove
singularities in the DOS agree excellently with magnetoresistance oscillations,
confirming that the model describes adequately the magnetoresistance of
strongly coupled semiconductor superlattices.Comment: 4 pages, 3 figures, elsart/PHYEAUTH macros; presented on the EP2DS-16
Conference in Albuquerque, New Mexico USA. To be published in Physica
Brownian motion in a non-homogeneous force field and photonic force microscope
The Photonic Force Microscope (PFM) is an opto-mechanical technique based on
an optical trap that can be assumed to probe forces in microscopic systems.
This technique has been used to measure forces in the range of pico- and
femto-Newton, assessing the mechanical properties of biomolecules as well as of
other microscopic systems. For a correct use of the PFM, the force field to
measure has to be invariable (homogeneous) on the scale of the Brownian motion
of the trapped probe. This condition implicates that the force field must be
conservative, excluding the possibility of a rotational component. However,
there are cases where these assumptions are not fulfilled Here, we show how to
improve the PFM technique in order to be able to deal with these cases. We
introduce the theory of this enhanced PFM and we propose a concrete analysis
workflow to reconstruct the force field from the experimental time-series of
the probe position. Furthermore, we experimentally verify some particularly
important cases, namely the case of a conservative or rotational force-field
Magnetotransport in graphene on silicon side of SiC
We have studied the transport properties of graphene grown on silicon side of
SiC. Samples under study have been prepared by two different growth methods in
two different laboratories. Magnetoresistance and Hall resistance have been
measured at temperatures between 4 and 100 K in resistive magnet in magnetic
fields up to 22 T. In spite of differences in sample preparation, the field
dependence of resistances measured on both sets of samples exhibits two periods
of magneto-oscillations indicating two different parallel conducting channels
with different concentrations of carriers. The semi-quantitative agreement with
the model calculation allows for conclusion that channels are formed by
high-density and low-density Dirac carriers. The coexistence of two different
groups of carriers on the silicon side of SiC was not reported before.Comment: 5 pages, 6 figures, accepted for publication in the "IOP Journal of
Physics: Conference series" as a contribution to the proceedings of the 20th
International Conference on "High Magnetic Fields in Semiconductor Physics",
HMF 2
Twenty years of BRCA1 and BRCA2 molecular analysis at MMCI : current developments for the classification of variants
The Bolocam Galactic Plane Survey. XII. Distance Catalog Expansion Using Kinematic Isolation of Dense Molecular Cloud Structures With 13CO(1-0)
We present an expanded distance catalog for 1,710 molecular cloud structures
identified in the Bolocam Galactic Plane Survey (BGPS) version 2, representing
a nearly threefold increase over the previous BGPS distance catalog. We
additionally present a new method for incorporating extant data sets into our
Bayesian distance probability density function (DPDF) methodology. To augment
the dense-gas tracers (e.g., HCO+(3-2), NH3(1,1)) used to derive line-of-sight
velocities for kinematic distances, we utilize the Galactic Ring Survey
13CO(1-0) data to morphologically extract velocities for BGPS sources. The
outline of a BGPS source is used to select a region of the GRS 13CO data, along
with a reference region to subtract enveloping diffuse emission, to produce a
line profile of 13CO matched to the BGPS source. For objects with a HCO+(3-2)
velocity, \approx 95% of the new 13CO(1-0) velocities agree with that of the
dense gas. A new prior DPDF for kinematic distance ambiguity (KDA) resolution,
based on a validated formalism for associating molecular cloud structures with
known objects from the literature, is presented. We demonstrate this prior
using catalogs of masers with trigonometric parallaxes and HII regions with
robust KDA resolutions. The distance catalog presented here contains
well-constrained distance estimates for 20% of BGPS V2 sources, with typical
distance uncertainties \lesssim 0.5 kpc. Approximately 75% of the
well-constrained sources lie within 6 kpc of the Sun, concentrated in the
Scutum-Centarus arm. Galactocentric positions of objects additionally trace out
portions of the Sagittarius, Perseus, and Outer arms in the first and second
Galactic quadrants, and we also find evidence for significant regions of
interarm dense gas.Comment: 28 pages, 19 figures. Accepted for publication in ApJ.
Distance-Omnibus code available at https://github.com/BGPS/distance-omnibu
Stimulation of beta-adrenergic receptors of S49 lymphoma cells redistributes the alpha subunit of the stimulatory G protein between cytosol and membranes.
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