27,345 research outputs found
Fractional statistics in the fractional quantum Hall effect
A microscopic confirmation of the fractional statistics of the {\em
quasiparticles} in the fractional quantum Hall effect has so far been lacking.
We calculate the statistics of the composite-fermion quasiparticles at
and by evaluating the Berry phase for a closed loop
encircling another composite-fermion quasiparticle. A careful consideration of
subtle perturbations in the trajectory due to the presence of an additional
quasiparticle is crucial for obtaining the correct value of the statistics. The
conditions for the applicability of the fractional statistics concept are
discussed.Comment: Phys. Rev. Lett., in pres
Laser heterodyne system for obtaining height profiles of minor species in the atmosphere
An infrared laser heterodyne system for obtaining height profiles of minor constituents of the atmosphere was developed and erected. A brief discription of the system is given. The system consists of a tunable CO2 waveguide laser in the 9 to 11 micrometer band, that is used as a local oscillator and a heliostat that follows the sun and brings in solar radiation, that is mixed with the laser beam in a high speed liquid nitrogen cooled mercury cadmium telluride detector. The detected signal is analysed in a RF spectrum analyser that allows tracing absorption line profiles. Absorption lines of a number of minor constituents in the troposphere and stratosphere, such as O3, NH3, H2O, SO2, ClO, N2O, are in the 9 to 11 micrometer band and overlap with that of CO2 laser range. The experimental system has been made operational and trial observations taken. Current measurements are limited to ozone height profiles. Results are presented
Logarithmic temperature dependence of conductivity at half-integer filling factors: Evidence for interaction between composite fermions
We have studied the temperature dependence of diagonal conductivity in
high-mobility two-dimensional samples at filling factors and 3/2 at
low temperatures. We observe a logarithmic dependence on temperature, from our
lowest temperature of 13 mK up to 400 mK. We attribute the logarithmic
correction to the effects of interaction between composite fermions, analogous
to the Altshuler-Aronov type correction for electrons at zero magnetic field.
The paper is accepted for publication in Physical Review B, Rapid
Communications.Comment: uses revtex macro
Activation gaps for the fractional quantum Hall effect: realistic treatment of transverse thickness
The activation gaps for fractional quantum Hall states at filling fractions
are computed for heterojunction, square quantum well, as well as
parabolic quantum well geometries, using an interaction potential calculated
from a self-consistent electronic structure calculation in the local density
approximation. The finite thickness is estimated to make 30% correction
to the gap in the heterojunction geometry for typical parameters, which
accounts for roughly half of the discrepancy between the experiment and
theoretical gaps computed for a pure two dimensional system. Certain model
interactions are also considered. It is found that the activation energies
behave qualitatively differently depending on whether the interaction is of
longer or shorter range than the Coulomb interaction; there are indications
that fractional Hall states close to the Fermi sea are destabilized for the
latter.Comment: 32 pages, 13 figure
Lorentz shear modulus of a two-dimensional electron gas at high magnetic field
We show that the Lorentz shear modulus -- one of the three elastic moduli of
a homogeneous electron gas in a magnetic field -- can be calculated exactly in
the limit of high magnetic field (i.e. in the lowest Landau level). Its value
is , where is the two-dimensional electron density and the
sign is determined by the orientation of the magnetic field. We use this result
to refine our previous calculations of the dispersion of the collective modes
of fractional quantum Hall liquids.Comment: 4 pages, 1 figur
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
Spin Transition in the Half-Filled Landau Level
The transition from partial to complete spin polarization of two-dimensional
electrons at half filling of the lowest Landau level has been studied using
resistively-detected nuclear magnetic resonance (RDNMR). The nuclear
spin-lattice relaxation time is observed to be density independent in the
partially polarized phase but to increase sharply at the transition to full
polarization. At low temperatures the RDNMR signal exhibits a strong maximum
near the critical density.Comment: 4 pages, 3 postscript figures. As published in Phys. Rev. Lett. 98,
086801 (2007
Cumulative effect of Forbush decreases in the heliospheric modulation during the present solar cycle
A monthly Forbush decrease index (Fd-I) is generated and it is compared with the observed long term chnges in the cosmic ray intensity near earth at energies greater than or equal to 1 Gev over 1976-83. Significant correlation is observed between the two except for 1978. Such an effect is also seen in the correlation plot between the solar flare index (SFI) and Fd-I
Evolutionary dynamics of the most populated genotype on rugged fitness landscapes
We consider an asexual population evolving on rugged fitness landscapes which
are defined on the multi-dimensional genotypic space and have many local
optima. We track the most populated genotype as it changes when the population
jumps from a fitness peak to a better one during the process of adaptation.
This is done using the dynamics of the shell model which is a simplified
version of the quasispecies model for infinite populations and standard
Wright-Fisher dynamics for large finite populations. We show that the
population fraction of a genotype obtained within the quasispecies model and
the shell model match for fit genotypes and at short times, but the dynamics of
the two models are identical for questions related to the most populated
genotype. We calculate exactly several properties of the jumps in infinite
populations some of which were obtained numerically in previous works. We also
present our preliminary simulation results for finite populations. In
particular, we measure the jump distribution in time and find that it decays as
as in the quasispecies problem.Comment: Minor changes. To appear in Phys Rev
Emulating Non-Abelian Topological Matter in Cold Atom Optical Lattices
Certain proposed extended Bose-Hubbard models may exhibit topologically
ordered ground states with excitations obeying non-Abelian braid statistics. A
sufficient tuning of Hubbard parameters could yield excitation braiding rules
allowing implementation of a universal set of topologically protected quantum
gates. We discuss potential difficulties in realizing a model with a proposed
non-Abelian topologically ordered ground state using optical lattices
containing bosonic dipoles. Our direct implementation scheme does not realize
the necessary anisotropic hopping, anisotropic interactions, and low
temperatures
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