4,542 research outputs found
Dynamical Kohn Anomaly in Surface Acoustic Wave Response in Quantum Hall Systems Near
The dynamical analog of the Kohn Anomaly image of the Fermi Surface is
demonstrated for the response functions to the surface acoustic waves in
Quantum Hall Systems near . Kinks appear in the velocity shift
and attenuation coefficient . The effect is considerably
enhanced under periodic modulation and should be observable.Comment: 5 pages, 2 figures, the published versio
Capital Mobility for Developing Countries May Not Be So High
International capital flows to developing countries have taken on considerable policy importance in recent years. There is disagreement, however, about whether financial capital mobility has become so high that developing countries have little ability to sterilize capital flows. This paper reviews several popular methods of estimating the degree of capital mobility for developing countries and shows that they are subject to potentially important upward biases due to inappropriate assumptions concerning the roles of domestic inflation and sterilization. Corrections for these factors can cut estimates of capital mobility by one half or more.sterilization; capital mobility; developing countries
Measurement of filling factor 5/2 quasiparticle interference: observation of charge e/4 and e/2 period oscillations
A standing problem in low dimensional electron systems is the nature of the
5/2 fractional quantum Hall state: its elementary excitations are a focus for
both elucidating the state's properties and as candidates in methods to perform
topological quantum computation. Interferometric devices may be employed to
manipulate and measure quantum Hall edge excitations. Here we use a small area
edge state interferometer designed to observe quasiparticle interference
effects. Oscillations consistent in detail with the Aharanov-Bohm effect are
observed for integer and fractional quantum Hall states (filling factors 2,
5/3, and 7/3) with periods corresponding to their respective charges and
magnetic field positions. With these as charge calibrations, at 5/2 filling
factor and at lowest temperatures periodic transmission through the device
consistent with quasiparticle charge e/4 is observed. The principal finding of
this work is that in addtion to these e/4 oscillations, periodic structures
corresponding to e/2 are also observed at 5/2 and at lowest temperatures.
Properties of the e/4 and e/2 oscillations are examined with the device
sensitivity sufficient to observe temperature evolution of the 5/2
quasiparticle interference. In the model of quasiparticle interference, this
presence of an effective e/2 period may empirically reflect an e/2
quasiparticle charge, or may reflect multiple passes of the e/4 quasiparticle
around the interferometer. These results are discussed within a picture of e/4
quasiparticle excitations potentially possessing non-Abelian statistics. These
studies demonstrate the capacity to perform interferometry on 5/2 excitations
and reveal properties important for understanding this state and its
excitations.Comment: version 3 contains additional data beyond version 2, 26 pages, 8
figures PNAS 081259910
Experimental Demonstration of Fermi Surface Effects at Filling Factor 5/2
Using small wavelength surface acoustic waves (SAW) on ultra-high mobility
heterostructures, Fermi surface properties are detected at 5/2 filling factor
at temperatures higher than those at which the quantum Hall state forms. An
enhanced conductivity is observed at 5/2 by employing sub 0.5 micron wavelength
SAW, indicating a quasiparticle mean-free-path substantially smaller than that
in the lowest Landau level. These findings are consistent with the presence of
a filled Fermi sea of composite fermions, which may pair at lower temperatures
to form the 5/2 ground state.Comment: 11 pages, 4 figure
Atmospheric constraint statistics for the Space Shuttle mission planning
The procedures used to establish statistics of atmospheric constraints of interest to the Space Shuttle mission planning are presented. The statistics considered are for the frequency of occurrence, runs, and time conditional probabilities of several atmospheric constrants for each of the Space Shuttle mission phases. The mission phases considered are (1) prelaunch, (2) launch, (3) return to launch site, (4) abort once around landing, and (5) end of mission landing
Beyond the Fermi Liquid Paradigm: Hidden Fermi Liquids
An intense investigation of possible non-Fermi liquid states of matter has
been inspired by two of the most intriguing phenomena discovered in the past
quarter century, namely high temperature superconductivity and the fractional
quantum Hall effect. Despite enormous conceptual strides, these two fields have
developed largely along separate paths. Two widely employed theories are the
resonating valence bond theory for high temperature superconductivity and the
composite fermion theory for the fractional quantum Hall effect. The goal of
this "perspective" article is to note that they subscribe to a common
underlying paradigm: they both connect these exotic quantum liquids to certain
ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation
yields numerous nontrivial experimental consequences, exposing these theories
to rigorous and definitive tests.Comment: perspective articl
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