772 research outputs found
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
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
Non-Abelian statistics in the interference noise of the Moore-Read quantum Hall state
We propose noise oscillation measurements in a double point contact,
accessible with current technology, to seek for a signature of the non-abelian
nature of the \nu=5/2 quantum Hall state. Calculating the voltage and
temperature dependence of the current and noise oscillations, we predict the
non-abelian nature to materialize through a multiplicity of the possible
outcomes: two qualitatively different frequency dependences of the nonzero
interference noise. Comparison between our predictions for the Moore-Read state
with experiments on \nu=5/2 will serve as a much needed test for the nature of
the \nu=5/2 quantum Hall state.Comment: 4 pages, 4 figures v2: typo's corrected, discussions clarified,
references adde
Noise and Full Counting Statistics of Incoherent Multiple Andreev Reflection
We present a general theory for the full counting statistics of multiple
Andreev reflections in incoherent superconducting-normal-superconducting
contacts. The theory, based on a stochastic path integral approach, is applied
to a superconductor-double barrier system. It is found that all cumulants of
the current show a pronounced subharmonic gap structure at voltages
. For low voltages , the counting statistics
results from diffusion of multiple charges in energy space, giving the th
cumulant , diverging for . We show that this
low-voltage result holds for a large class of incoherent
superconducting-normal-superconducting contacts.Comment: 4 pages, 4 figure
La participación de los empleados en España : ¿cuánto, cómo y en qué participan?.
En este trabajo aportamos evidencia empírica acerca de la participación de los empleados en la toma de decisiones de la empresa. Utilizamos una base de datos (EPOC) de más de 5700 establecimiento de toda Europa, y comparamos la situación española con la del resto de países europeos. La riqueza de la encuesta nos permite conocer múltiples detalles sobre los niveles de participación, los tipos de prácticas de participación utilizadas, las cuestiones sobre los empleados opinan o deciden, y las fechas en que estas prácticas fueron adoptadas.Participación de los empleados;
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