456 research outputs found
Shot noise suppression in multimode ballistic Fermi conductors
We have derived a general formula describing current noise in multimode
ballistic channels connecting source and drain electrodes with Fermi electron
gas. In particular (at ), the expression describes the
nonequilibrium ''shot'' noise, which may be suppressed by both Fermi
correlations and space charge screening. The general formula has been applied
to an approximate model of a 2D nanoscale, ballistic MOSFET. At large negative
gate voltages, when the density of electrons in the channel is small, shot
noise spectral density approaches the Schottky value , where
is the average current. However, at positive gate voltages, when the
maximum potential energy in the channel is below the Fermi level of the
electron source, the noise can be at least an order of magnitude smaller than
the Schottky value, mostly due to Fermi effects.Comment: 4 page
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
Microscopic analysis of shot-noise suppression in nondegenerate diffusive conductors
We present a theoretical investigation of shot-noise suppression due to
long-range Coulomb interaction in nondegenerate diffusive conductors.
Calculations make use of an ensemble Monte Carlo simulator self-consistently
coupled with a one-dimensional Poisson solver. We analyze the noise in a
lightly doped active region surrounded by two contacts acting as thermal
reservoirs. By taking the doping of the injecting contacts and the applied
voltage as variable parameters, the influence of elastic and inelastic
scattering in the active region is investigated. The transition from ballistic
to diffusive transport regimes under different contact injecting statistics is
analyzed and discussed. Provided significant space-charge effects take place
inside the active region, long-range Coulomb interaction is found to play an
essential role in suppressing the shot noise at . In the elastic
diffusive regime, momentum space dimensionality is found to modify the
suppression factor , which within numerical uncertainty takes values
respectively of about 1/3, 1/2 and 0.7 in the 3D, 2D and 1D cases. In the
inelastic diffusive regime, shot noise is suppressed to the thermal value.Comment: 11 pages, 13 figure
Shot-noise anomalies in nondegenerate elastic diffusive conductors
We present a theoretical investigation of shot-noise properties in
nondegenerate elastic diffusive conductors. Both Monte Carlo simulations and
analytical approaches are used. Two new phenomena are found: (i) the display of
enhanced shot noise for given energy dependences of the scattering time, and
(ii) the recovery of full shot noise for asymptotic high applied bias. The
first phenomenon is associated with the onset of negative differential
conductivity in energy space that drives the system towards a dynamical
electrical instability in excellent agreement with analytical predictions. The
enhancement is found to be strongly amplified when the dimensionality in
momentum space is lowered from 3 to 2 dimensions. The second phenomenon is due
to the suppression of the effects of long range Coulomb correlations that takes
place when the transit time becomes the shortest time scale in the system, and
is common to both elastic and inelastic nondegenerate diffusive conductors.
These phenomena shed new light in the understanding of the anomalous behavior
of shot noise in mesoscopic conductors, which is a signature of correlations
among different current pulses.Comment: 9 pages, 6 figures. Final version to appear in Phys. Rev.
Nonlinear voltage dependence of the shot noise in mesoscopic degenerate conductors with strong electron-electron scattering
It is shown that measurements of zero-frequency shot-noise can provide
information on electron-electron interaction, because the strong interaction
results in the nonlinear voltage dependence of the shot noise in metallic
wires. This is due to the fact that the Wiedemann-Franz law is no longer valid
in the case of considerable electron-electron interaction. The deviations from
this law increase the noise power and make it dependent strongly on the ratio
of electron-electron and electron-impurity scattering rates.Comment: 4 pages, 2 figures, revised version according to referee's comment
Coulomb screening in mesoscopic noise: a kinetic approach
Coulomb screening, together with degeneracy, is characteristic of the
metallic electron gas. While there is little trace of its effects in transport
and noise in the bulk, at mesoscopic scales the electronic fluctuations start
to show appreciable Coulomb correlations. Within a strictly standard Boltzmann
and Fermi-liquid framework, we analyze these phenomena and their relation to
the mesoscopic fluctuation-dissipation theorem, which we prove. We identify two
distinct screening mechanisms for mesoscopic fluctuations. One is the
self-consistent response of the contact potential in a non-uniform system. The
other couples to scattering, and is an exclusively non-equilibrium process.
Contact-potential effects renormalize all thermal fluctuations, at all scales.
Collisional effects are relatively short-ranged and modify non-equilibrium
noise. We discuss ways to detect these differences experimentally.Comment: Source: REVTEX. 16 pp.; 7 Postscript figs. Accepted for publication
in J. Phys.: Cond. Ma
Dynamical effects of an unconventional current-phase relation in YBCO dc-SQUIDs
The predominant d-wave pairing symmetry in high temperature superconductors
allows for a variety of current-phase relations in Josephson junctions, which
is to a certain degree fabrication controlled. In this letter we report on
direct experimental observations of the effects of a non-sinusoidal
current-phase dependence in YBCO dc-SQUIDs, which agree with the theoretical
description of the system.Comment: 4 pages, 4 ps figures, to apprear in Phys. Rev. Let
Universal distribution of transparencies in highly conductive Nb/AlO/Nb junctions
We report the observation of the universal distribution of transparencies,
predicted by Schep and Bauer [Phys. Rev. Lett. {\bf 78}, 3015 (1997)] for dirty
sharp interfaces, in uniform Nb/AlO/Nb junctions with high specific
conductance ( Ohmcm). Experiments used the BCS density of
states in superconducting niobium for transparency distribution probing.
Experimental results for both the dc curves at magnetic-field-suppressed
supercurrent and the Josephson critical current in zero magnetic field coincide
remarkably well with calculations based on the multimode theory of multiple
Andreev reflections and the Schep-Bauer distribution.Comment: 4 pages, 4 figures, references adde
Charge Fluctuations in Quantum Point Contacts and Chaotic Cavities in the Presence of Transport
We analyze the frequency-dependent current fluctuations induced into a gate
near a quantum point contact or a quantum chaotic cavity. We use a current and
charge conserving, effective scattering approach in which interactions are
treated in random phase approximation. The current fluctuations measured at a
nearby gate, coupled capacitively to the conductor, are determined by the
screened charge fluctuations of the conductor. Both the equilibrium and the
non-equilibrium current noise at the gate can be expressed with the help of
resistances which are related to the charge dynamics on the conductor. We
evaluate these resistances for a point contact and determine their
distributions for an ensemble of chaotic cavities. For a quantum point contact
these resistances exhibit pronounced oscillations with the opening of new
channels. For a chaotic cavity coupled to one channel point contacts the charge
relaxation resistance shows a broad distribution between 1/4 and 1/2 of a
resistance quantum. The non-equilibrium resistance exhibits a broad
distribution between zero and 1/4 of a resistance quantum.Comment: 9 pages, two-column Revtex, 6 figures include
Suppression of non-Poissonian shot noise by Coulomb correlations in ballistic conductors
We investigate the current injection into a ballistic conductor under the
space-charge limited regime, when the distribution function of injected
carriers is an arbitrary function of energy F_c(epsilon). The analysis of the
coupled kinetic and Poisson equations shows that the injected current
fluctuations may be essentially suppressed by Coulomb correlations, and the
suppression level is determined by the shape of F_c(epsilon). This is in
contrast to the time-averaged quantities: the mean current and the spatial
profiles are shown to be insensitive to F_c(epsilon) in the leading-order terms
at high biases. The asymptotic high-bias behavior for the energy resolved
shot-noise suppression has been found for an arbitrary (non-Poissonian)
injection, which may suggest a new field of investigation on the optimization
of the injected energy profile to achieve the desired noise-suppression level.Comment: extended version 4 -> 8 pages, examples and figure adde
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