1,900 research outputs found
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
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
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
Steady States of a Microwave Irradiated Quantum Hall Gas
We consider effects of a long-wavelength disorder potential on the Zero
Conductance State (ZCS) of the microwave-irradiated 2D electron gas. Assuming a
uniform Hall conductivity, we construct a Lyapunov functional and derive
stability conditions on the domain structure of the photo-generated fields. We
solve the resulting equations for a general one-dimensional and certain
two-dimensional disorder potentials, and find non-zero conductances,
photo-voltages, and circulating dissipative currents. In contrast, weak white
noise disorder does not destroy the ZCS, but induces mesoscopic current
fluctuations.Comment: 4 pages, 2 colour figure
Stability and effective masses of composite-fermions in the first and second Landau Level
We propose a measure of the stability of composite fermions (CF's) at
even-denominator Landau-level filling fractions. Assuming Landau-level mixing
effects are not strong, we show that the CF liquid at in the
Landau level cannot exist and relate this to the absence of a hierarchy of
incompressible states for filling fractions . We find that
a polarized CF liquid should exist at . We also show that, for CF
states, the variation with system size of the ground state energy of
interacting electrons follows that for non-interacting particles in zero
magnetic field. We use this to estimate the CF effective masses.Comment: 9 pages, Revtex, PSIZ-TP-940
A Fermi Fluid Description of the Half-Filled Landau Level
We present a many-body approach to calculate the ground state properties of a
system of electrons in a half-filled Landau level. Our starting point is a
simplified version of the recently proposed trial wave function where one
includes the antisymmetrization operator to the bosonic Laughlin state. Using
the classical plasma analogy, we calculate the pair-correlation function, the
static structure function and the ground state energy in the thermodynamic
limit. These results are in good agreement with the expected behavior at
.Comment: 4 pages, REVTEX, and 4 .ps file
One-Dimensional Theory of the Quantum Hall System
We consider the lowest Landau level on a torus as a function of its
circumference . When , the ground state at general rational
filling fraction is a crystal with a gap--a Tao-Thouless state. For filling
fractions , these states are the limits of Laughlin's or Jain's
wave functions describing the gapped quantum Hall states when .
For the half-filled Landau level, there is a transition to a Fermi sea of
non-interacting neutral dipoles, or rather to a Luttinger liquid modification
thereof, at magnetic lengths. This state is a version of the
Rezayi-Read state, and develops continuously into the state that is believed to
describe the observed metallic phase as . Furthermore, the
effective Landau level structure that emerges within the lowest Landau level
follows from the magnetic symmetries.Comment: 4 pages, 1 figur
Dynamical Correlations in a Half-Filled Landau Level
We formulate a self-consistent field theory for the Chern-Simons fermions to
study the dynamical response function of the quantum Hall system at .
Our scheme includes the effect of correlations beyond the random-phase
approximation (RPA) employed to this date for this system. The resulting
zero-frequency density response function vanishes as the square of the wave
vector in the long-wavelength limit. The longitudinal conductivity calculated
in this scheme shows linear dependence on the wave vector, like the
experimentals results and the RPA, but the absolute values are higher than the
experimental results.Comment: 4 pages, revtex, 3 figures included. Corrected typo
Local Geometry of the Fermi Surface and Magnetoacoustic Responce of Two-Dimensional Electron Systems in Strong Magnetic Fields
A semiclassical theory for magnetotrasport in a quantum Hall system near
filling factor based on the Composite Fermions physical picture is
used to analyze the effect of local flattening of the Composite Fermion Fermi
surface (CF-FS) upon magnetoacoustic oscllations. We report on calculations of
the velocity shift and attenuation of a surface acoustic wave (SAW) which
travels above the two-dimensional electron system, and we show that local
geometry of the CF-FS could give rise to noticeable changes in the magnitude
and phase of the oscillations. We predict these changes to be revealed in
experiments, and to be used in further studies of the shape and symmetries of
the CF-FS. Main conclusions reported here could be applied to analyze
magnetotransport in quantum Hall systems at higher filling factors provided the Fermi-liquid-like state of the system.Comment: 7 pages, 2 figure
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