473 research outputs found
Quantum Theory of Flicker Noise in Metal Films
Flicker (1/f^gamma) voltage noise spectrum is derived from finite-temperature
quantum electromagnetic fluctuations produced by elementary charge carriers in
external electric field. It is suggested that deviations of the frequency
exponent \gamma from unity, observed in thin metal films, can be attributed to
quantum backreaction of the conducting medium on the fluctuating field of the
charge carrier. This backreaction is described phenomenologically in terms of
the effective momentum space dimensionality, D. Using the dimensional
continuation technique, it is shown that the combined action of the photon heat
bath and external field results in a 1/f^gamma-contribution to the spectral
density of the two-point correlation function of electromagnetic field. The
frequency exponent is found to be equal to 1 + delta, where delta = 3 - D is a
reduction of the momentum space dimensionality. This result is applied to the
case of a biased conducting sample, and a general expression for the voltage
power spectrum is obtained which possesses all characteristic properties of
observed flicker noise spectra. The range of validity of this expression covers
well the whole measured frequency band. Gauge independence of the power
spectrum is proved. It is shown that the obtained results naturally resolve the
problem of divergence of the total noise power. A detailed comparison with the
experimental data on flicker noise measurements in metal films is given.Comment: 20 pages, 2 tables, 2 figure
Effect of long-range Coulomb interaction on shot-noise suppression in ballistic transport
We present a microscopic analysis of shot-noise suppression due to long-range
Coulomb interaction in semiconductor devices under ballistic transport
conditions. An ensemble Monte Carlo simulator self-consistently coupled with a
Poisson solver is used for the calculations. A wide range of injection-rate
densities leading to different degrees of suppression is investigated. A sharp
tendency of noise suppression at increasing injection densities is found to
scale with a dimensionless Debye length related to the importance of
space-charge effects in the structure.Comment: RevTex, 4 pages, 4 figures, minor correction
Shot Noise Suppression in Avalanche Photodiodes
We identify a new shot noise suppression mechanism in a thin (~100 nm)
heterostructure avalanche photodiode. In the low-gain regime the shot noise is
suppressed due to temporal correlations within amplified current pulses. We
demonstrate in a Monte Carlo simulation that the effective excess noise factors
can be <1, and reconcile the apparent conflict between theory and experiments.
This shot noise suppression mechanism is independent of known mechanisms such
as Coulomb interaction, or reflection at heterojunction interfaces.Comment: Phys. Rev. Lett., accepted for publicatio
Statistical theory of shot noise in quasi-1D Field Effect Transistors in the presence of electron-electron interaction
We present an expression for the shot noise power spectral density in
quasi-one dimensional conductors electrostatically controlled by a gate
electrode, that includes the effects of Coulomb interaction and of Pauli
exclusion among charge carriers. In this sense, our expression extends the well
known Landauer-Buttiker noise formula to include the effect of Coulomb
interaction through induced fluctuations in the device potential. Our approach
is based on the introduction of statistical properties of the scattering matrix
and on a second-quantization many-body description. From a quantitative point
of view, statistical properties are obtained by means of Monte Carlo
simulations on a ensemble of different configurations of injected states,
requiring the solution of the Poisson-Schrodinger equation on a
three-dimensional grid, with the non-equilibrium Green functions formalism. In
a series of example, we show that failure to consider the effects of Coulomb
interaction on noise leads to a gross overestimation of the noise spectrum of
quasi-one dimensional devices
Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors
We predict the existence of an anomalous crossover between thermal and shot
noise in macroscopic diffusive conductors. We first show that, besides thermal
noise, these systems may also exhibit shot noise due to fluctuations of the
total number of carriers in the system. Then we show that at increasing
currents the crossover between the two noise behaviors is anomalous, in the
sense that the low frequency current spectral density displays a region with a
superlinear dependence on the current up to a cubic law. The anomaly is due to
the non-trivial coupling in the presence of the long range Coulomb interaction
among the three time scales relevant to the phenomenon, namely, diffusion,
transit and dielectric relaxation time.Comment: 4 pages, 2 figure
Low frequency shot noise in double-barrier resonant-tunneling structures in a strong magnetic field
Low frequency shot noise and dc current profiles for a double-barrier
resonant-tunneling structure (DBRTS) under a strong magnetic field applied
perpendicular to the interfaces have been studied. Both the structures with 3D
and 2D emitter have been considered. The calculations, carried out with the
Keldysh Green's function technique, show strong dependencies of both the
current and noise profiles on the bias voltage and magnetic field. The noise
spectrum appears sensitive to charge accumulation due to barriere capacitances
and both noise and dc-current are extremely sensitive to the Landau levels'
broadening in the emitter electrode and can be used as a powerful tool to
investigate the latter. As an example, two specific shapes of the levels'
broadening have been considered - a semi-elliptic profile resulting from
self-consistent Born approximation, and a Gaussian one resulting from the
lowest order cumulant expansion.Comment: 15 pages Revtex, 8 Postscript figures included. To be published in
Journal of Physics: Condensed matte
Scaling of 1/f noise in tunable break-junctions
We have studied the voltage noise of gold nano-contacts in
electromigrated and mechanically controlled break-junctions having resistance
values that can be tuned from 10 (many channels) to 10 k
(single atom contact). The noise is caused by resistance fluctuations as
evidenced by the dependence of the power spectral density
on the applied DC voltage . As a function of the normalized noise
shows a pronounced cross-over from for low-ohmic
junctions to for high-ohmic ones. The measured powers of 3
and 1.5 are in agreement with -noise generated in the bulk and reflect the
transition from diffusive to ballistic transport
Shot Noise in Linear Macroscopic Resistors
We report on a direct experimental evidence of shot noise in a linear
macroscopic resistor. The origin of the shot noise comes from the fluctuation
of the total number of charge carriers inside the resistor associated with
their diffusive motion under the condition that the dielectric relaxation time
becomes longer than the dynamic transit time. Present results show that neither
potential barriers nor the absence of inelastic scattering are necessary to
observe shot noise in electronic devices.Comment: 10 pages, 5 figure
- …