45 research outputs found
Interannual variations of water mass properties and volumes in the Southern Ocean
International audienceTime-resolving optimum multi-parameter (TROMP) analysis is used to study interannual variability of water mass properties in the Southern Ocean in a section between Antarctica and Tasmania for the period 1991?1996. Water mass properties were stable during 1994?1996 but showed departures from their 1994-1996 values during 1991 and 1993. TROMP analysis is unable to quantify the interannual variation in detail, but it is shown that interannual variability does not invalidate the findings of a previous study that was based on the assumption of time-invariable water mass properties and suggested large interannual fluctuations in the water mass volumes south of Tasmania
Effect of screening on shot noise in diffusive mesoscopic conductors
Shot noise in diffusive mesoscopic conductors, at finite observation
frequencies (comparable to the reciprocal Thouless time
), is analyzed with an account of screening. At low frequencies,
the well-known result is recovered. This result is valid at
arbitrary for wide conductors longer than the screening length.
However, at least for two very different systems, namely, wide and short
conductors, and thin conductors over a close ground plane, noise approaches a
different fundamental level, , at .Comment: 5 pages, 3 figures. Published version. Also available in the
journal's format at
http://hana.physics.sunysb.edu/~yehuda/cv/papers/shotnoise.pd
Towards single-electron metrology
We review the status of the understanding of single-electron transport (SET)
devices with respect to their applicability in metrology. Their envisioned role
as the basis of a high-precision electrical standard is outlined and is
discussed in the context of other standards. The operation principles of single
electron transistors, turnstiles and pumps are explained and the fundamental
limits of these devices are discussed in detail. We describe the various
physical mechanisms that influence the device uncertainty and review the
analytical and numerical methods needed to calculate the intrinsic uncertainty
and to optimise the fabrication and operation parameters. Recent experimental
results are evaluated and compared with theoretical predictions. Although there
are discrepancies between theory and experiments, the intrinsic uncertainty is
already small enough to start preparing for the first SET-based metrological
applications.Comment: 39 pages, 14 figures. Review paper to be published in International
Journal of Modern Physics
Nonuniversal Shot Noise in Disordered Quantum Wires with Channel-Number Imbalance
The number of conducting channels for one propagating direction is equal to
that for the other direction in ordinary quantum wires. However, they can be
imbalanced in graphene nanoribbons with zigzag edges. Employing the model
system in which a degree of channel-number imbalance can be controlled, we
calculate the shot-noise power at zero frequency by using the
Boltzmann-Langevin approach. The shot-noise power in an ordinary diffusive
conductor is one-third of the Poisson value. We show that with increasing the
degree of channel-number imbalance, the universal one-third suppression breaks
down and a highly nonuniversal behavior of shot noise appears.Comment: 10 pages, 3 figure
Current fluctuations in a single tunnel junction
We study noise spectra of currents through a tunnel junction in weak
tunneling limit. We introduce effective capacitance to take into account the
interaction effect and explicitly incorporate the electromagnetic environment
of the junction into the formulation. We study the effect of charging energy
and macroscopic environment on noise spectra. We calculate current fluctuations
at tunneling barrier and fluctuations measured at leads. It is shown that two
fluctuations have different noise spectra and the relation between them is
nontrivial. We provide an explanation for the origin of the difference.
Experimental implications are discussed.Comment: 25 pages, Revtex 3.
Universality of the 1/3 shot-noise suppression factor in nondegenerate diffusive conductors
Shot-noise suppression is investigated in nondegenerate diffusive conductors
by means of an ensemble Monte Carlo simulator. The universal 1/3 suppression
value is obtained when transport occurs under elastic collision regime provided
the following conditions are satisfied: (i) The applied voltage is much larger
than the thermal value; (ii) the length of the device is much longer than both
the elastic mean free path and the Debye length. By fully suppressing
carrier-number fluctuations, long range Coulomb interaction is essential to
obtain the 1/3 value in the low-frequency limit.Comment: RevTex, 4 pages, 4 figure
Universality of Shot-Noise in Multiterminal Diffusive Conductors
We prove the universality of shot-noise in multiterminal diffusive conductors
of arbitrary shape and dimension for purely elastic scattering as well as for
hot electrons. Using a Boltzmann-Langevin approach we reduce the calculation of
shot-noise correlators to the solution of a diffusion equation. We show that
shot-noise in multiterminal conductors is a non-local quantity and that
exchange effects can occur without quantum phase coherence even at zero
electron temperature. Concrete numbers for shot-noise are given that can be
tested experimentally.Comment: 4 double-column pages, REVTeX, 1 eps figure embedded with eps
The 1/3-shot noise suppression in diffusive nanowires
We report low-temperature shot noise measurements of short diffusive Au wires
attached to electron reservoirs of varying sizes. The measured noise
suppression factor compared to the classical noise value
strongly depends on the electric heat conductance of the reservoirs. For small
reservoirs injection of hot electrons increases the measured noise and hence
the suppression factor. The universal 1/3-suppression factor can only
asymptotically be reached for macroscopically large and thick electron
reservoirs. A heating model based on the Wiedemann-Franz law is used to explain
this effect.Comment: 10 figure
Current noise in long diffusive SNS junctions in the incoherent MAR regime
Spectral density of current fluctuations at zero frequency is calculated for
a long diffusive SNS junction with low-resistive interfaces. At low
temperature, T << Delta, the subgap shot noise approaches linear voltage
dependence, S=(2/ 3R)(eV + 2Delta), which is the sum of the shot noise of the
normal conductor and voltage independent excess noise. This result can also be
interpreted as the 1/3-suppressed Poisson noise for the effective charge q =
e(1+2Delta/eV) transferred by incoherent multiple Andreev reflections (MAR). At
higher temperatures, anomalies of the current noise develop at the gap
subharmonics, eV = 2Delta/n. The crossover to the hot electron regime from the
MAR regime is analyzed in the limit of small applied voltages.Comment: improved version, to be published in Phys. Rev.
Semiclassical theory of shot-noise suppression
The Boltzmann-Langevin equation is used to relate the shot-noise power of a
mesoscopic conductor to classical transmission probabilities at the Fermi
level. This semiclassical theory is applied to tunneling through n barriers in
series. For n -> infinity the shot noise approaches one third of the Poisson
noise, independent of the transparency of the barriers. This confirms that the
one-third suppression known to occur in diffusive conductors does not require
phase coherence.Comment: pages, RevTeX, 1 figur