16,103 research outputs found
Primary-Filling e/3 Quasiparticle Interferometer
We report experimental realization of a quasiparticle interferometer where
the entire system is in 1/3 primary fractional quantum Hall state. The
interferometer consists of chiral edge channels coupled by quantum-coherent
tunneling in two constrictions, thus enclosing an Aharonov-Bohm area. We
observe magnetic flux and charge periods h/e and e/3, equivalent to creation of
one quasielectron in the island. Quantum theory predicts a 3h/e flux period for
charge e/3, integer statistics particles. Accordingly, the observed periods
demonstrate the anyonic statistics of Laughlin quasiparticles
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
Electron interferometry in quantum Hall regime: Aharonov-Bohm effect of interacting electrons
An apparent h/fe Aharonov-Bohm flux period, where f is an integer, has been
reported in coherent quantum Hall devices. Such sub-period is not expected for
non-interacting electrons and thus is thought to result from interelectron
Coulomb interaction. Here we report experiments in a Fabry-Perot interferometer
comprised of two wide constrictions enclosing an electron island. By carefully
tuning the constriction front gates, we find a regime where interference
oscillations with period h/2e persist throughout the transition between the
integer quantum Hall plateaus 2 and 3, including half-filling. In a large
quantum Hall sample, a transition between integer plateaus occurs near
half-filling, where the bulk of the sample becomes delocalized and thus
dissipative bulk current flows between the counterpropagating edges
("backscattering"). In a quantum Hall constriction, where conductance is due to
electron tunneling, a transition between forward- and back-scattering is
expected near the half-filling. In our experiment, neither period nor amplitude
of the oscillations show a discontinuity at half-filling, indicating that only
one interference path exists throughout the transition. We also present
experiments and an analysis of the front-gate dependence of the phase of the
oscillations. The results point to a single physical mechanism of the observed
conductance oscillations: Aharonov-Bohm interference of interacting electrons
in quantum Hall regime.Comment: 10 pages, 4 Fig
Characterizing the Hofstadter butterfly's outline with Chern numbers
In this work, we report original properties inherent to independent particles
subjected to a magnetic field by emphasizing the existence of regular
structures in the energy spectrum's outline. We show that this fractal curve,
the well-known Hofstadter butterfly's outline, is associated to a specific
sequence of Chern numbers that correspond to the quantized transverse
conductivity. Indeed the topological invariant that characterizes the
fundamental energy band depicts successive stairways as the magnetic flux
varies. Moreover each stairway is shown to be labeled by another Chern number
which measures the charge transported under displacement of the periodic
potential. We put forward the universal character of these properties by
comparing the results obtained for the square and the honeycomb geometries.Comment: Accepted for publication in J. Phys. B (Jan 2009
Realization of a Laughlin quasiparticle interferometer: Observation of fractional statistics
In two dimensions, the laws of physics permit existence of anyons, particles
with fractional statistics which is neither Fermi nor Bose. That is, upon
exchange of two such particles, the quantum state of a system acquires a phase
which is neither 0 nor \pi, but can be any value. The elementary excitations
(Laughlin quasiparticles) of a fractional quantum Hall fluid have fractional
electric charge and are expected to obey fractional statistics. Here we report
experimental realization of a novel Laughlin quasiparticle interferometer,
where quasiparticles of the 1/3 fluid execute a closed path around an island of
the 2/5 fluid and thus acquire statistical phase. Interference fringes are
observed as conductance oscillations as a function of magnetic flux, similar to
the Aharonov-Bohm effect. We observe the interference shift by one fringe upon
introduction of five magnetic flux quanta (5h/e) into the island. The
corresponding 2e charge period is confirmed directly in calibrated gate
experiments. These results constitute direct observation of fractional
statistics of Laughlin quasiparticles.Comment: manuscript of the long version published in Phys. Rev.
MoodBar: Increasing new user retention in Wikipedia through lightweight socialization
Socialization in online communities allows existing members to welcome and
recruit newcomers, introduce them to community norms and practices, and sustain
their early participation. However, socializing newcomers does not come for
free: in large communities, socialization can result in a significant workload
for mentors and is hard to scale. In this study we present results from an
experiment that measured the effect of a lightweight socialization tool on the
activity and retention of newly registered users attempting to edit for the
first time Wikipedia. Wikipedia is struggling with the retention of newcomers
and our results indicate that a mechanism to elicit lightweight feedback and to
provide early mentoring to newcomers improves their chances of becoming
long-term contributors.Comment: 9 pages, 5 figures, accepted for presentation at CSCW'1
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