1,338 research outputs found
Subtraction of test mass angular noise in the LISA Technology Package interferometer
We present recent sensitivity measurements of the LISA Technology Package
interferometer with articulated mirrors as test masses, actuated by
piezo-electric transducers. The required longitudinal displacement resolution
of 9 pm/sqrt[Hz] above 3 mHz has been demonstrated with an angular noise that
corresponds to the expected in on-orbit operation. The excess noise
contribution of this test mass jitter onto the sensitive displacement readout
was completely subtracted by fitting the angular interferometric data streams
to the longitudinal displacement measurement. Thus, this cross-coupling
constitutes no limitation to the required performance of the LISA Technology
Package interferometry.Comment: Applied Physics B - Lasers and Optics (2008
In-plane gate single-electron transistor in Ga[Al]As fabricated by scanning probe lithography
A single-electron transistor has been realized in a Ga[Al]As heterostructure
by oxidizing lines in the GaAs cap layer with an atomic force microscope. The
oxide lines define the boundaries of the quantum dot, the in-plane gate
electrodes, and the contacts of the dot to source and drain. Both the number of
electrons in the dot as well as its coupling to the leads can be tuned with an
additional, homogeneous top gate electrode. Pronounced Coulomb blockade
oscillations are observed as a function of voltages applied to different gates.
We find that, for positive top-gate voltages, the lithographic pattern is
transferred with high accuracy to the electron gas. Furthermore, the dot shape
does not change significantly when in-plane voltages are tuned.Comment: 4 pages, 3 figure
Transport properties of quantum dots with hard walls
Quantum dots are fabricated in a Ga[Al]As-heterostructure by local oxidation
with an atomic force microscope. This technique, in combination with top gate
voltages, allows us to generate steep walls at the confining edges and small
lateral depletion lengths. The confinement is characterized by low-temperature
magnetotransport measurements, from which the dots' energy spectrum is
reconstructed. We find that in small dots, the addition spectrum can
qualitatively be described within a Fock-Darwin model. For a quantitative
analysis, however, a hard-wall confinement has to be considered. In large dots,
the energy level spectrum deviates even qualitatively from a Fock-Darwin model.
The maximum wall steepness achieved is of the order of 0.4 meV/nm.Comment: 9 pages, 5 figure
Transport properties of quantum dots with hard walls
Quantum dots are fabricated in a Ga[Al]As-heterostructure by local oxidation
with an atomic force microscope. This technique, in combination with top gate
voltages, allows us to generate steep walls at the confining edges and small
lateral depletion lengths. The confinement is characterized by low-temperature
magnetotransport measurements, from which the dots' energy spectrum is
reconstructed. We find that in small dots, the addition spectrum can
qualitatively be described within a Fock-Darwin model. For a quantitative
analysis, however, a hard-wall confinement has to be considered. In large dots,
the energy level spectrum deviates even qualitatively from a Fock-Darwin model.
The maximum wall steepness achieved is of the order of 0.4 meV/nm.Comment: 9 pages, 5 figure
Generic suppression of conductance quantization of interacting electrons in graphene nanoribbons in a perpendicular magnetic field
The effects of electron interaction on the magnetoconductance of graphene
nanoribbons (GNRs) are studied within the Hartree approximation. We find that a
perpendicular magnetic field leads to a suppression instead of an expected
improvement of the quantization. This suppression is traced back to
interaction-induced modifications of the band structure leading to the
formation of compressible strips in the middle of GNRs. It is also shown that
the hard wall confinement combined with electron interaction generates overlaps
between forward and backward propagating states, which may significantly
enhance backscattering in realistic GNRs. The relation to available experiments
is discussed.Comment: 4 pages, 3 figure
Electronic properties of antidot lattices fabricated by atomic force lithography
Antidot lattices were fabricated by atomic force lithography using local
oxidation. High quality finite 20 x20 lattices are demonstrated with periods of
300 nm. The low temperature magnetoresistance shows well developed
commensurability oscillations as well as a quenching of the Hall effect around
zero magnetic field. In addition, we find B periodic oscillations superimposed
on the classical commensurability peaks at temperatures as high as 1.7 K. These
observations indicate the high electronic quality of our samples.Comment: Appl. Phys. Lett., in prin
Measuring random force noise for LISA aboard the LISA Pathfinder mission
The LTP (LISA Testflight Package), to be flown aboard the ESA / NASA LISA
Pathfinder mission, aims to demonstrate drag-free control for LISA test masses
with acceleration noise below 30 fm/s^2/Hz^1/2 from 1-30 mHz. This paper
describes the LTP measurement of random, position independent forces acting on
the test masses. In addition to putting an overall upper limit for all source
of random force noise, LTP will measure the conversion of several key
disturbances into acceleration noise and thus allow a more detailed
characterization of the drag-free performance to be expected for LISA.Comment: 7 pages, 3 figures. To be published in Classical and Quantum Gravity
with the proceedings of the 2003 Amaldi Meetin
Filament absorption study using THEMIS and SOHO/CDS-SUMER observations
A long filament has been observed with THEMIS/MSDP and
SOHO/CDS-SUMER, during a coordinated campaign (JOPs 131/95) on May 5, 2000. THEMIS provided 2D Hα spectra, SUMER rasters in the L4 line and spectra of the whole Lymanseries and the Lymancon tinuum, CDS obtained rasters in several EUV lines (e.g., Mg X 624 ˚A, Si XII 520 ˚A, Ca X 557 ˚A and He I 584 ˚A). A large depression of coronal line emission in the CDS images corresponds to the absorption by the hydrogen Lyman continuum and represents the EUV filament. Non-LTE radiative transfer calculations allow to explain, in terms of opacities, the large width of the EUV filament compared to the width of the Hα filament itself.
The optical thickness of the Lyman continuum is larger than that of Hα line by one to two orders of magnitude. This could be of great importance in the understanding of the filament formation, if we consider that cool material does exist in filament channels but is optically too thin to be visible in Hα images
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