648 research outputs found
Composite Fermions and Landau Level Mixing in the Fractional Quantum Hall Effect
The reduction of the energy gap due to Landau level mixing, characterized by
the dimensionless parameter , has
been calculated by variational Monte Carlo for the fractional quantum Hall
effect at filling fractions and 1/5 using a modified version of
Jain's composite fermion wave functions. These wave functions exploit the
Landau level mixing already present in composite fermion wave functions by
introducing a partial Landau level projection operator. Results for the energy
gaps are consistent with experimental observations in -type GaAs, but we
conclude that Landau level mixing alone cannot account for the significantly
smaller energy gaps observed in -type systems.Comment: 11 pages, RevTex, 2 figures in compressed tar .ps forma
Composite fermions traversing a potential barrier
Using a composite fermion picture, we study the lateral transport between two
two-dimensional electron gases, at filling factor 1/2, separated by a potential
barrier. In the mean field approximation, composite fermions far from the
barrier do not feel a magnetic field while in the barrier region the effective
magnetic field is different from zero. This produces a cutoff in the
conductance when represented as a function of the thickness and height of the
barrier. There is a range of barrier heights for which an incompressible
liquid, at , exists in the barrier region.Comment: 3 pages, latex, 4 figures available upon request from
[email protected]. To appear in Physical Review B (RC) June 15t
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
Fractional quantum Hall effect in higher Landau levels
We investigate, using finite size numerical calculations, the spin-polarized
fractional quantum Hall effect (FQHE) in the first excited Landau level (LL).
We find evidence for the existence of an incompressible state at , but not at . Surprisingly,
the 7/3 state is found to be strongest at a finite thickness. The structure of
the low- lying excited states is found to be markedly different from that in
the lowest LL. This study also rules out FQHE at a large number of
odd-denominator fractions in the lowest LL.Comment: 7 pages RevTex, 4 figure
Composite Fermions and the Energy Gap in the Fractional Quantum Hall Effect
The energy gaps for the fractional quantum Hall effect at filling fractions
1/3, 1/5, and 1/7 have been calculated by variational Monte Carlo using Jain's
composite fermion wave functions before and after projection onto the lowest
Landau level. Before projection there is a contribution to the energy gaps from
the first excited Landau level. After projection this contribution vanishes,
the quasielectron charge becomes more localized, and the Coulomb energy
contribution increases. The projected gaps agree well with previous
calculations, lending support to the composite fermion theory.Comment: 12 pages, Revtex 3.0, 2 compressed and uuencoded postscript figures
appended, NHMFL-94-062
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
Quantum corrections to the conductivity of fermion - gauge field models: Application to half filled Landau level and high- superconductors
We calculate the Altshuler-Aronov type quantum correction to the conductivity
of charge carriers in a random potential (or random magnetic field)
coupled to a transverse gauge field. The gauge fields considered simulate the
effect of the Coulomb interaction for the fractional quantum Hall state at half
filling and for the model of high- superconducting compounds. We
find an unusually large quantum correction varying linearly or quadratically
with the logarithm of temperature, in different temperature regimes.Comment: 12 pages REVTEX, 1 figure. The figure is added and minor misprints
are correcte
Fractional Quantum Hall States in Low-Zeeman-Energy Limit
We investigate the spectrum of interacting electrons at arbitrary filling
factors in the limit of vanishing Zeeman splitting. The composite fermion
theory successfully explains the low-energy spectrum {\em provided the
composite fermions are treated as hard-core}.Comment: 12 pages, revte
Hund's Rule for Composite Fermions
We consider the ``fractional quantum Hall atom" in the vanishing Zeeman
energy limit, and investigate the validity of Hund's maximum-spin rule for
interacting electrons in various Landau levels. While it is not valid for {\em
electrons} in the lowest Landau level, there are regions of filling factors
where it predicts the ground state spin correctly {\em provided it is applied
to composite fermions}. The composite fermion theory also reveals a
``self-similar" structure in the filling factor range .Comment: 10 pages, revte
Magnetoroton instabilities and static susceptibilities in higher Landau levels
We present analytical results concerning the magneto-roton instability in
higher Landau levels evaluated in the single mode approximation. The roton gap
appears at a finite wave vector, which is approximately independent of the LL
index n, in agreement with numerical calculations in the composite-fermion
picture. However, a large maximum in the static susceptibility indicates a
charge density modulation with wave vectors , as
expected from Hartree-Fock predictions. We thus obtain a unified description of
the leading charge instabilities in all LLs.Comment: 4 pages, 5 figure
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