5,961 research outputs found
Very low shot noise in carbon nanotubes
We have performed noise measurements on suspended ropes of single wall carbon
nanotubes (SWNT) between 1 and 300 K for different values of dc current through
the ropes. We find that the shot noise is suppressed by more than a factor 100
compared to the full shot noise 2eI. We have also measured an individual SWNT
and found a level of noise which is smaller than the minimum expected. Another
finding is the very low level of 1/f noise, which is significantly lower than
previous observations. We propose two possible interpretations for this strong
shot noise reduction: i) Transport within a rope takes place through a few
nearly ballistic tubes within a rope and possibly involves non integer
effective charges. ii) A substantial fraction of the tubes conduct with a
strong reduction of effective charge (by more than a factor 50).Comment: Submitted to Eur. Phys. J. B (Jan. 2002) Higher resolution pictures
are posted on http://www.lps.u-psud.fr/Collectif/gr_07/publications.htm
Vortex density spectrum of quantum turbulence
The fluctuations of the vortex density in a turbulent quantum fluid are
deduced from local second-sound attenuation measurements. These measurements
are performed with a micromachined open-cavity resonator inserted across a flow
of turbulent He-II near 1.6 K. The power spectrum of the measured vortex line
density is compatible with a (-5/3) power law. The physical interpretation,
still open, is discussed.Comment: Submitted to Europhys. Let
New Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55
As part of a wider investigation of evolved massive stars in Galactic open clusters, we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51, Berkeley 55 and NGC 6603. Using new multi-epoch photometry, we confirm that Be 51 #162 and Be 55 #107 are bona fide Cepheids, with pulsation periods of 9.83±0.01 d and 5.850±0.005 d respectively, while NGC 6603 star W2249 does not show significant photometric variability. Using the period-luminosity relationship for Cepheid variables, we determine a distance to Be 51 of 5.3 +1.0 −0.8 kpc and an age of 44 +9 −8 Myr, placing it in a sparsely-attested region of the Perseus arm. For Be 55, we find a distance of 2.2±0.3 kpc and age of 63 +12 −11 Myr, locating the cluster in the Local arm. Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222, these represent an important increase in the number of young, massive Cepheids known in Galactic open clusters. We also consider new Gaia (data release 2) parallaxes and proper motions for members of Be 51 and Be 55; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters, but the well-constrained proper motion measurements furnish further confirmation of cluster membership. However, future final Gaia parallaxes for such objects should provide valuable independent distance measurements, improving the calibration of the period-luminosity relationship, with implications for the distance ladder out to cosmological scales
Intrinsic and extrinsic decay of edge magnetoplasmons in graphene
We investigate intrinsic and extrinsic decay of edge magnetoplasmons (EMPs)
in graphene quantum Hall (QH) systems by high-frequency electronic
measurements. From EMP resonances in disk shaped graphene, we show that the
dispersion relation of EMPs is nonlinear due to interactions, giving rise to
intrinsic decay of EMP wavepacket. We also identify extrinsic dissipation
mechanisms due to interaction with localized states in bulk graphene from the
decay time of EMP wavepackets. We indicate that, owing to the unique linear and
gapless band structure, EMP dissipation in graphene can be lower than that in
GaAs systems.Comment: 5 page
Effect of interactions on the noise of chiral Luttinger liquid systems
We analyze the current noise, generated at a quantum point contact in
fractional quantum Hall edge state devices, using the chiral Luttinger liquid
model with an impurity and the associated exact field theoretic solution. We
demonstrate that an experimentally relevant regime of parameters exists where
the noise coincides with the partition noise of independent Laughlin
quasiparticles. However, outside of this regime, this independent particle
picture breaks down and the inclusion of interaction effects is essential to
understand the shot noise.Comment: 4 pages, 3 figures; v2: modified FIG.1, new FIG.
Effects of magnetic field and disorder on electronic properties of Carbon Nanotubes
Electronic properties of metallic and semiconducting carbon nanotubes are
investigated in presence of magnetic field perpendicular to the CN-axis, and
disorder introduced through energy site randomness. The magnetic field field is
shown to induce a metal-insulator transition (MIT) in absence of disorder, and
surprisingly disorder does not affect significantly the MIT. These results may
find confirmation through tunneling experimentsComment: 4 pages, 6 figures. Phys. Rev. B (in press
Quantum coherence engineering in the integer quantum Hall regime
We present an experiment where the quantum coherence in the edge states of
the integer quantum Hall regime is tuned with a decoupling gate. The coherence
length is determined by measuring the visibility of quantum interferences in a
Mach-Zehnder interferometer as a function of temperature, in the quantum Hall
regime at filling factor two. The temperature dependence of the coherence
length can be varied by a factor of two. The strengthening of the phase
coherence at finite temperature is shown to arise from a reduction of the
coupling between co-propagating edge states. This opens the way for a strong
improvement of the phase coherence of Quantum Hall systems. The decoupling gate
also allows us to investigate how inter-edge state coupling influence the
quantum interferences' dependence on the injection bias. We find that the
finite bias visibility can be decomposed into two contributions: a Gaussian
envelop which is surprisingly insensitive to the coupling, and a beating
component which, on the contrary, is strongly affected by the coupling.Comment: 4 pages, 5 figure
Multi time and space scale monitoring of the sand extraction and its impact on the seabed by coupling EMS data and MBES measurements
- …