930 research outputs found
Experimental Evidence for a Spin-Polarized Ground State in the \nu=5/2 Fractional Quantum Hall Effect
We study the \nu=5/2 even-denominator fractional quantum Hall effect (FQHE)
over a wide range of magnetic (B) field in a heterojunction insulated gate
field-effect transistor (HIGFET). The electron density can be tuned from n=0 to
7.6 \times 10^{11} cm^{-2} with a peak mobility \mu = 5.5 \times 10^6 cm^2/Vs.
The \nu=5/2 state shows a strong minimum in diagonal resistance and a
developing Hall plateau at magnetic fields as high as 12.6T. The strength of
the energy gap varies smoothly with B-field. We interpret these observations as
strong evidence for a spin-polarized ground state at \nu=5/2.Comment: new references adde
An assessment of the strength of knots and splices used as eye terminations in a sailing environment
Research into knots, splices and other methods of forming an eye termination has been limited, despite the fact that they are essential and strongly affect the performance of a rope. The aim of this study was to carry out a comprehensive initial assessment of the breaking strength of eye terminations commonly used in a sailing environment, thereby providing direction for further work in the field. Supports for use in a regular tensile testing machine were specially developed to allow individual testing of each sample and a realistic spread of statistical data to be obtained. Over 180 break tests were carried out on four knots (the bowline, double bowline, figure-of-eight loop and perfection loop) and two splices (three-strand eye splice and braid-on-braid splice). The factors affecting their strength were investigated. A statistical approach to the analysis of the results was adopted. The type of knot was found to have a significant effect on the strength. This same effect was seen in both types of rope construction (three-strand and braid-on-braid). Conclusions were also drawn as to the effect of splice length, eye size, manufacturer and rope diameter on the breaking strength of splices. Areas of development and further investigation were identified
Partially spin polarized quantum Hall effect in the filling factor range 1/3 < nu < 2/5
The residual interaction between composite fermions (CFs) can express itself
through higher order fractional Hall effect. With the help of diagonalization
in a truncated composite fermion basis of low-energy many-body states, we
predict that quantum Hall effect with partial spin polarization is possible at
several fractions between and . The estimated excitation
gaps are approximately two orders of magnitude smaller than the gap at
, confirming that the inter-CF interaction is extremely weak in higher
CF levels.Comment: 4 pages, 3 figure
Multilevel Semantic Analysis and Problem-Solving in the Flight Domain: Final Report: NASA Grant NCCI-52, July 11, 1981-July 10, 1982
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryNASA Grant NCCI-5
Electron correlation energy in confined two-electron systems
Radial, angular and total correlation energies are calculated for four
two-electron systems with atomic numbers Z=0-3 confined within an impenetrable
sphere of radius R. We report accurate results for the non-relativistic,
restricted Hartree-Fock and radial limit energies over a range of confinement
radii from 0.05 - 10 a0. At small R, the correlation energies approach limiting
values that are independent of Z while at intermediate R, systems with Z > 1
exhibit a characteristic maximum in the correlation energy resulting from an
increase in the angular correlation energy which is offset by a decrease in the
radial correlation energy
Mixed States of Composite Fermions Carrying Two and Four Vortices
There now exists preliminary experimental evidence for some fractions, such
as = 4/11 and 5/13, that do not belong to any of the sequences
, and being integers. We propose that these states
are mixed states of composite fermions of different flavors, for example,
composite fermions carrying two and four vortices. We also obtain an estimate
of the lowest-excitation dispersion curve as well as the transport gap; the
gaps for 4/11 are smaller than those for 1/3 by approximately a factor of 50.Comment: Accepted for PRB rapid communication (scheduled to appear in Nov 15,
2000 issue
Specific heat of quasi-2D antiferromagnetic Heisenberg models with varying inter-planar couplings
We have used the stochastic series expansion (SSE) quantum Monte Carlo (QMC)
method to study the three-dimensional (3D) antiferromagnetic Heisenberg model
on cubic lattices with in-plane coupling J and varying inter-plane coupling
J_perp < J. The specific heat curves exhibit a 3D ordering peak as well as a
broad maximum arising from short-range 2D order. For J_perp << J, there is a
clear separation of the two peaks. In the simulations, the contributions to the
total specific heat from the ordering across and within the layers can be
separated, and this enables us to study in detail the 3D peak around T_c (which
otherwise typically is dominated by statistical noise). We find that the peak
height decreases with decreasing J_perp, becoming nearly linear below J_perp =
0.2J. The relevance of these results to the lack of observed specific heat
anomaly at the ordering transition of some quasi-2D antiferromagnets is
discussed.Comment: 7 pages, 8 figure
Structures for Interacting Composite Fermions: Stripes, Bubbles, and Fractional Quantum Hall Effect
Much of the present day qualitative phenomenology of the fractional quantum
Hall effect can be understood by neglecting the interactions between composite
fermions altogether. For example the fractional quantum Hall effect at
corresponds to filled composite-fermion Landau levels,and
the compressible state at to the Fermi sea of composite fermions.
Away from these filling factors, the residual interactions between composite
fermions will determine the nature of the ground state. In this article, a
model is constructed for the residual interaction between composite fermions,
and various possible states are considered in a variational approach. Our study
suggests formation of composite-fermion stripes, bubble crystals, as well as
fractional quantum Hall states for appropriate situations.Comment: 16 pages, 7 figure
Dynamics of Void and its Shape in Redshift Space
We investigate the dynamics of a single spherical void embedded in a
Friedmann-Lema\^itre universe, and analyze the void shape in the redshift
space. We find that the void in the redshift space appears as an ellipse shape
elongated in the direction of the line of sight (i.e., an opposite deformation
to the Kaiser effect). Applying this result to observed void candidates at the
redshift z~1-2, it may provide us with a new method to evaluate the
cosmological parameters, in particular the value of a cosmological constant.Comment: 19 pages, 11 figure
Density and well width dependences of the effective mass of twodimensional holes in (100) GaAs quantum wells measured by cyclotron resonance at microwave frequencies
Cyclotron resonance at microwave frequencies is used to measure the band mass
(m_b) of the two-dimensional holes (2DH's) in carbon-doped (100)
GaAs/AlxGa1-xAs heterostructures. The measured m_b shows strong dependences on
both the 2DH density(p) and the GaAs quantum well width (W). For a fixed W, in
the density range (0.4x10^11 to 1.1x10^11 cm^-2) studied here, m_b increases
with p, consistent with previous studies of the 2DHs on the (311)A surface. For
a fixed p = 1.1x10^11 cm^-2, mb increases from 0.22 m_e at W = 10 nm to 0.50
m_e at W = 30 nm, and saturates around 0.51 m_e for W > 30 nm.Comment: to appear in Solid State Communication
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