76 research outputs found
Resonant Enhancement of Inelastic Light Scattering in the Fractional Quantum Hall Regime at
Strong resonant enhancements of inelastic light scattering from the long
wavelength inter-Landau level magnetoplasmon and the intra-Landau level spin
wave excitations are seen for the fractional quantum Hall state at .
The energies of the sharp peaks (FWHM ) in the profiles of
resonant enhancement of inelastic light scattering intensities coincide with
the energies of photoluminescence bands assigned to negatively charged exciton
recombination. To interpret the observed enhancement profiles, we propose
three-step light scattering mechanisms in which the intermediate resonant
transitions are to states with charged excitonic excitations.Comment: 5 pages, 5 figure
Splitting of Long-Wavelength Modes of the Fractional Quantum Hall Liquid at
Resonant inelastic light scattering experiments at reveal a novel
splitting of the long wavelength modes in the low energy spectrum of
quasiparticle excitations in the charge degree of freedom. We find a single
peak at small wavevectors that splits into two distinct modes at larger
wavevectors. The evidence of well-defined dispersive behavior at small
wavevectors indicates a coherence of the quantum fluid in the micron length
scale. We evaluate interpretations of long wavelength modes of the electron
liquid.Comment: 4 pages, 4 figure
Spin texture and magnetoroton excitations at nu=1/3
Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020 +/- 0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3
Transition from Free to Interacting Composite Fermions away from =1/3
Spin excitations from a partially populated composite fermion level are
studied above and below . In the range the experiments
uncover significant departures from the non-interacting composite fermion
picture that demonstrate the increasing impact of interactions as quasiparticle
Landau levels are filled. The observed onset of a transition from free to
interacting composite fermions could be linked to condensation into the higher
order states suggested by transport experiments and numerical evaluations
performed in the same filling factor range.Comment: 4 pages, 5 figures, to appear in PR
Spin excitations in the Fractional Quantum Hall regime at
We report inelastic light scattering experiments in the fractional quantum
Hall regime at filling factors . A spin mode is observed below
the Zeeman energy. The filling factor dependence of the mode energy is
consistent with its assignment to spin flip excitations of composite fermions
with four attached flux quanta (=4). Our findings reveal a composite
fermion Landau level structure in the =4 sequence.Comment: 7 pages, 4 figures, EP2DS-16 conference, to appear in Physica
Gauge Theory of Composite Fermions: Particle-Flux Separation in Quantum Hall Systems
Fractionalization phenomenon of electrons in quantum Hall states is studied
in terms of U(1) gauge theory. We focus on the Chern-Simons(CS) fermion
description of the quantum Hall effect(QHE) at the filling factor
, and show that the successful composite-fermions(CF) theory
of Jain acquires a solid theoretical basis, which we call particle-flux
separation(PFS). PFS can be studied efficiently by a gauge theory and
characterized as a deconfinement phenomenon in the corresponding gauge
dynamics. The PFS takes place at low temperatures, , where
each electron or CS fermion splinters off into two quasiparticles, a fermionic
chargeon and a bosonic fluxon. The chargeon is nothing but Jain's CF, and the
fluxon carries units of CS fluxes. At sufficiently low temperatures , fluxons Bose-condense uniformly and (partly)
cancel the external magnetic field, producing the correlation holes. This
partial cancellation validates the mean-field theory in Jain's CF approach.
FQHE takes place at as a joint effect of (i) integer QHE of
chargeons under the residual field and (ii) Bose condensation of
fluxons. We calculate the phase-transition temperature and the CF
mass. PFS is a counterpart of the charge-spin separation in the t-J model of
high- cuprates in which each electron dissociates into holon and
spinon. Quasiexcitations and resistivity in the PFS state are also studied. The
resistivity is just the sum of contributions of chargeons and fluxons, and
changes its behavior at , reflecting the change of
quasiparticles from chargeons and fluxons at to electrons at
.Comment: 18 pages, 7 figure
Higher-Energy Composite Fermion Levels in the Fractional Quantum Hall Effect
Even though composite fermions in the fractional quantum Hall liquid are well established, it is not yet known up to what energies they remain intact. We probe the high-energy spectrum of the 1/3 liquid directly by resonant inelastic light scattering, and report the observation of a large number of new collective modes. Supported by our theoretical calculations, we associate these with transitions across two or more composite fermions levels. The formation of quasiparticle levels up to high energies is direct evidence for the robustness of topological order in the fractional quantum Hall effect
Persistence with Statins and Onset of Rheumatoid Arthritis: A Population-Based Cohort Study
In a retrospective cohort study, Gabriel Chodick and colleagues find a significant association between persistence with statin therapy and reduced risk of developing rheumatoid arthritis, but only a modest decrease in risk of osteoarthritis
- …