868 research outputs found
Homiletics
Homiletics and Sermon Notes for the Ebenezer Festival Servic
Background problem in electron-energy-loss spectroscopy
At large scattering angle the background formation in electron-energy-loss spectroscopy is determined by elastic-inelastic scattering events. The suitability of the usual background fitting AE−r is critically investigated as a function of specimen thickness, collection angle, and width of energy window
Determination of the position maximum for electron Compton scattering in electron microscopy
We study electron Compton scattering with an electron microscope by means of a Castaing-Henry filter. In the electron-spectroscopic-diffraction mode the positions of the Compton maxima in the diffraction plane are determined. We find a nearly constant shift of this position with respect to the value given by E=q2/2. The intensity of Compton-scattered electrons does not peak at the scattering angle predicted by the binary collision mode. The energy dispersion of the Compton profile is well described by E=q2/2
Linear magnetoresistance in a quasi-free two dimensional electron gas in an ultra-high mobility GaAs quantum well
We report a magnetotransport study of an ultra-high mobility
(\,cm\,V\,s) -type GaAs
quantum well up to 33 T. A strong linear magnetoresistance (LMR) of the order
of 10 % is observed in a wide temperature range between 0.3 K and 60 K. The
simplicity of our material system with a single sub-band occupation and free
electron dispersion rules out most complicated mechanisms that could give rise
to the observed LMR. At low temperature, quantum oscillations are superimposed
onto the LMR. Both, the featureless LMR at high and the quantum
oscillations at low follow the empirical resistance rule which states that
the longitudinal conductance is directly related to the derivative of the
transversal (Hall) conductance multiplied by the magnetic field and a constant
factor that remains unchanged over the entire temperature range. Only
at low temperatures, small deviations from this resistance rule are observed
beyond that likely originate from a different transport mechanism for
the composite fermions
Constructive role of non-adiabaticity for quantized charge pumping
We investigate a recently developed scheme for quantized charge pumping based
on single-parameter modulation. The device was realized in an AlGaAl-GaAs gated
nanowire. It has been shown theoretically that non-adiabaticity is
fundamentally required to realize single-parameter pumping, while in previous
multi-parameter pumping schemes it caused unwanted and less controllable
currents. In this paper we demonstrate experimentally the constructive and
destructive role of non-adiabaticity by analysing the pumping current over a
broad frequency range.Comment: Presented at ICPS 2010, July 25 - 30, Seoul, Kore
Fabrication of quantum point contacts by engraving GaAs/AlGaAs-heterostructures with a diamond tip
We use the all-diamond tip of an atomic force microscope for the direct
engraving of high quality quantum point contacts in
GaAs/AlGaAs-heterostructures. The processing time is shortened by two orders of
magnitude compared to standard silicon tips. Together with a reduction of the
line width to below 90 nm the depletion length of insulating lines is reduced
by a factor of two with the diamond probes. The such fabricated defect free
ballistic constrictions show well resolved conductance plateaus and the 0.7
anomaly in electronic transport measurements.Comment: 3 pages, 3 figure
Magneto Seebeck effect in REFeAsO (RE=rare earth) compounds: probing the magnon drag scenario
We investigate Seebeck effect in REFeAsO (RE=rare earth)compounds as a
function of temperature and magnetic field up to 30T. The Seebeck curves are
characterized by a broad negative bump around 50K, which is sample dependent
and strongly enhanced by the application of a magnetic field. A model for the
temperature and field dependence of the magnon drag contribution to the Seebeck
effect by antiferromagnetic (AFM) spin fluctuation is developed. It accounts
for the magnitude and scaling properties of such bump feature in our
experimental data. This analysis allows to extract precious information on the
coupling between electrons and AFM spin fluctuations in these parent compound
systems, with implications on the pairing mechanism of the related
superconducting compounds
Quantum resistance metrology in graphene
We have performed a metrological characterization of the quantum Hall
resistance in a 1 m wide graphene Hall-bar. The longitudinal resistivity
in the center of the quantum Hall plateaus vanishes within the
measurement noise of 20 m upto 2 A. Our results show that the
quantization of these plateaus is within the experimental uncertainty (15 ppm
for 1.5A current) equal to that in conventional semiconductors. The
principal limitation of the present experiments are the relatively high contact
resistances in the quantum Hall regime, leading to a significantly increased
noise across the voltage contacts and a heating of the sample when a high
current is applied
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