778 research outputs found
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
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
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
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
Recent progress in the development of few mode fiber amplifier
We review the performances of both core and cladding pumped few-mode erbium doped fiber amplifiers supporting 6 spatial modes (4 mode groups) which incidentally the highest mode count demonstrated to date
Characterization of fractional-quantum-Hall-effect quasiparticles
Composite fermions in a partially filled quasi-Landau level may be viewed as
quasielectrons of the underlying fractional quantum Hall state, suggesting that
a quasielectron is simply a dressed electron, as often is true in other
interacting electron systems, and as a result has the same intrinsic charge and
exchange statistics as an electron. This paper discusses how this result is
reconciled with the earlier picture in which quasiparticles are viewed as
fractionally-charged fractional-statistics ``solitons". While the two
approaches provide the same answers for the long-range interactions between the
quasiparticles, the dressed-electron description is more conventional and
unifies the view of quasiparticle dynamics in and beyond the fractional quantum
Hall regime.Comment: 11 pages, latex, no figure
Cosmic-ray acceleration in supernova remnants: non-linear theory revised
A rapidly growing amount of evidences, mostly coming from the recent
gamma-ray observations of Galactic supernova remnants (SNRs), is seriously
challenging our understanding of how particles are accelerated at fast shocks.
The cosmic-ray (CR) spectra required to account for the observed phenomenology
are in fact as steep as , i.e., steeper than the
test-particle prediction of first-order Fermi acceleration, and significantly
steeper than what expected in a more refined non-linear theory of diffusive
shock acceleration. By accounting for the dynamical back-reaction of the
non-thermal particles, such a theory in fact predicts that the more efficient
the particle acceleration, the flatter the CR spectrum. In this work we put
forward a self-consistent scenario in which the account for the magnetic field
amplification induced by CR streaming produces the conditions for reversing
such a trend, allowing --- at the same time --- for rather steep spectra and CR
acceleration efficiencies (about 20%) consistent with the hypothesis that SNRs
are the sources of Galactic CRs. In particular, we quantitatively work out the
details of instantaneous and cumulative CR spectra during the evolution of a
typical SNR, also stressing the implications of the observed levels of
magnetization on both the expected maximum energy and the predicted CR
acceleration efficiency. The latter naturally turns out to saturate around
10-30%, almost independently of the fraction of particles injected into the
acceleration process as long as this fraction is larger than about .Comment: 24 pages, 5 figures, accepted for publication in JCA
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
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