3,611 research outputs found
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
Composite fermions in the Fractional Quantum Hall Effect: Transport at finite wavevector
We consider the conductivity tensor for composite fermions in a close to
half-filled Landau band in the temperature regime where the scattering off the
potential and the trapped gauge field of random impurities dominates. The
Boltzmann equation approach is employed to calculate the quasiclassical
transport properties at finite effective magnetic field, wavevector and
frequency. We present an exact solution of the kinetic equation for all
parameter regimes. Our results allow a consistent description of recently
observed surface acoustic wave resonances and other findings.Comment: REVTEX, 4 pages, 1 figur
Composite Fermions in Modulated Structures: Transport and Surface Acoustic Waves
Motivated by a recent experiment of Willett et al. [Phys. Rev. Lett. 78, 4478
(1997)], we employ semiclassical composite-fermion theory to study the effect
of a periodic density modulation on a quantum Hall system near Landau level
filling factor nu=1/2. We show that even a weak density modulation leads to
dramatic changes in surface-acoustic-wave (SAW) propagation, and propose an
explanation for several key features of the experimental observations. We
predict that properly arranged dc transport measurements would show a structure
similar to that seen in SAW measurements.Comment: Version published in Phys. Rev. Lett. Figures changed to show SAW
velocity shift. LaTeX, 5 pages, two included postscript figure
Effective mass of composite fermion: a phenomenological fit in with anomalous propagation of surface acoustic wave
We calculate the conductivity associated with the anomalous propagation of a
surface acoustic wave above a two-dimensional electron gas at .
Murthy-Shankar's middle representation is adopted and a contribution to the
response functions beyond the random phase approximation has been taken into
account. We give a phenomenological fit for the effective mass of composite
fermion in with the experimental data of the anomalous propagation of surface
acoustic wave at and find the phenomenological value of the effective
mass is several times larger than the theoretical value
derived from the Hartree-Fock approximation. We
compare our phenomenologically fitting composite fermion effective mass with
those appeared in the measurements of the activation energy and the
Shubnikov-de Haas effect and find that our result is fairly reasonable.Comment: 8 pages, 5 figures, the longer version of cond-mat/9801131 with
crucial corrections, accepted for publication by PR
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
Magnetic field-tuned Aharonov-Bohm oscillations and evidence for non-Abelian anyons at v=5/2
We show that the resistance of the v=5/2 quantum Hall state, confined to an
interferometer, oscillates with magnetic field consistent with an Ising-type
non-Abelian state. In three quantum Hall interferometers of different sizes,
resistance oscillations at v=7/3 and integer filling factors have the magnetic
field period expected if the number of quasiparticles contained within the
interferometer changes so as to keep the area and the total charge within the
interferometer constant. Under these conditions, an Abelian state such as the
(3,3,1) state would show oscillations with the same period as at an integer
quantum Hall state. However, in an Ising-type non-Abelian state there would be
a rapid oscillation associated with the "even-odd effect" and a slower one
associated with the accumulated Abelian phase due to both the Aharonov-Bohm
effect and the Abelian part of the quasiparticle braiding statistics. Our
measurements at v=5/2 are consistent with the latter.Comment: 10 pages, 8 figures, includes Supplemental Material
Weiss Oscillations in Surface Acoustic Wave Propagation
The interaction of a surface acoustic wave (SAW) with a a two-dimensional
electron gas in a periodic electric potential and a classical magnetic field is
considered. We calculate the attenuation of the SAW and its velocity change and
show that these quantities exhibit Weiss oscillations.Comment: 4 pages REVTEX, 2 figures included as eps file
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