arXiv subjects

L. Reggiani

Publications and source records attributed to L. Reggiani.

At least 37 records · Page 2Linked to original sources

arXiv2004

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.

cond-mat.mtrl-sci↗

arXiv2004

Fluctuations of Complex Networks: Electrical Properties of Single Protein Nanodevices

We present for the first time a complex network approach to the study of the electrical properties of single protein devices. In particular, we consider an electronic nanobiosensor based on a G-protein coupled receptor. By adopting a coarse grain description, the protein is modeled as a complex network of elementary impedances. The positions of the alpha-carbon atoms of each amino acid are taken as the nodes of the network. The amino acids are assumed to interact electrically among them. Consequently, a link is drawn between any pair of nodes neighboring in space within a given distance and an elementary impedance is associated with each link. The value of this impedance can be related to the physical and chemical properties of the amino acid pair and to their relative distance. Accordingly, the conformational changes of the receptor induced by the capture of the ligand, are translated into a variation of its electrical properties. Stochastic fluctuations in the value of the elementary impedances of the network, which mimic different physical effects, have also been considered. Preliminary results concerning the impedance spectrum of the network and its fluctuations are presented and discussed for different values of the model parameters.

q-bio.MN↗

arXiv2004

A Biased Resistor Network Model for Electromigration Failure and Related Phenomena in Metallic Lines

Electromigration phenomena in metallic lines are studied by using a biased resistor network model. The void formation induced by the electron wind is simulated by a stochastic process of resistor breaking, while the growth of mechanical stress inside the line is described by an antagonist process of recovery of the broken resistors. The model accounts for the existence of temperature gradients due to current crowding and Joule heating. Alloying effects are also accounted for. Monte Carlo simulations allow the study within a unified theoretical framework of a variety of relevant features related to the electromigration. The predictions of the model are in excellent agreement with the experiments and in particular with the degradation towards electrical breakdown of stressed Al-Cu thin metallic lines. Detailed investigations refer to the damage pattern, the distribution of the times to failure (TTFs), the generalized Black's law, the time evolution of the resistance, including the early-stage change due to alloying effects and the electromigration saturation appearing at low current densities or for short line lengths. The dependence of the TTFs on the length and width of the metallic line is also well reproduced. Finally, the model successfully describes the resistance noise properties under steady state conditions.

cond-mat.stat-mech↗

arXiv2004

Non-Gaussian Resistance Noise near Electrical Breakdown in Granular Materials

The distribution of resistance fluctuations of conducting thin films with granular structure near electrical breakdown is studied by numerical simulations. The film is modeled as a resistor network in a steady state determined by the competition between two biased processes, breaking and recovery. Systems of different sizes and with different levels of internal disorder are considered. Sharp deviations from a Gaussian distribution are found near breakdown and the effect increases with the degree of internal disorder. However, we show that in general this non-Gaussianity is related to the finite size of the system and vanishes in the large size limit. Nevertheless, near the critical point of the conductor-insulator transition, deviations from Gaussianity persist when the size is increased and the distribution of resistance fluctuations is well fitted by the universal Bramwell-Holdsworth-Pinton distribution.

cond-mat.stat-mech↗

arXiv2003

A quantum coherent approach to transport and noise in double barrier resonant diodes: shot noise a way to distinguish coherent from sequential tunneling

We implement a quantum approach which includes long range Coulomb interaction and investigate current voltage characteristics and shot noise in double barrier resonant diodes. Theory applies to the region of low applied voltages up to the region of the current peak and considers the wide temperature range from zero to room temperature. The shape of the current voltage characteristic is well reproduced and we confirm that even in the presence of Coulomb interaction shot noise can be suppressed with a Fano factor well below the value of 0.5. This feature is a signature of coherent tunnelling since the standard sequential tunnelling predicts in general a Fano factor equal to or greater than the value 0.5. This giant suppression is a consequence of Pauli principle as well as long range Coulomb interaction. The theory generalizes previous findings and is compared with experiments.

cond-mat.mes-hall↗

arXiv2003

Non-Gaussianity of resistance fluctuations near electrical breakdown

We study the resistance fluctuation distribution of a thin film near electrical breakdown. The film is modeled as a stationary resistor networkunder biased percolation. Depending on the value of the external current,on the system sizes and on the level of internal disorder, the fluctuation distribution can exhibit a non-Gaussian behavior. We analyze this non-Gaussianity in terms of the generalized Gumbel distribution recently introduced in the context of highly correlated systems near criticality. We find that when the average fraction of defects approaches the random percolation threshold, the resistance fluctuation distribution is well described by the universal behavior of the Bramwell-Holdsworth-Pinton distribution.

cond-mat↗

arXiv2003

A quantum generalization of the thermal viscous friction law

On the basis of the equivalence of the energy balance deacription at micro- and macro-level we propose a quantum generalization of the viscous friction law for a macroscopic Langevin equation describing thermal fluctuations without the zero point contribution. This equation recovers the classical case in the limit h -> 0. In particular it satisfies the quantum regression theorem and resolves several anomalies appearing in the quantum extension of the fluctuation dissipation theorem.

cond-mat.stat-mech↗

arXiv2002

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.

cond-mat.mes-hall↗

arXiv2002

Unipolar transport and shot noise in metal-semiconductor-metal structures

We carry out a self-consistent analytical theory of unipolar current and noise properties of metal-semiconductor-metal structures made of highly resistive semiconductors in the presence of an applied bias of arbitrary strength. By including the effects of the diffusion current we succeed to study the whole range of carrier injection conditions going from low level injection, where the structure behaves as a linear resistor, to high level injection, where the structure behaves as a space charge limited diode. We show that these structures display shot noise at the highest voltages. Remarkably the crossover from Nyquist noise to shot noise exhibits a complicate behavior with increasing current where an initial square root dependence (double thermal noise) is followed by a cubic power law.

cond-mat.stat-mech↗

arXiv2002

Size effects on generation recombination noise

We carry out an analytical theory of generation-recombination noise for a two level resistor model which goes beyond those presently available by including the effects of both space charge fluctuations and diffusion current. Finite size effects are found responsible for the saturation of the low frequency current spectral density at high enough applied voltages. The saturation behaviour is controlled essentially by the correlations coming from the long range Coulomb interaction. It is suggested that the saturation of the current fluctuations for high voltage bias constitutes a general feature of generation-recombination noise.

cond-mat.stat-mech↗

arXiv2002

Can quantum regression theorem be reconciled with quantum fluctuation dissipation theorem ?

In the attempt to derive the regression theorem from the fluctuation dissipation theorem several authors claim the violation of the former theorem in the quantum case. Here we pose the question: does it exists a quantum fluctuation dissipation theorem (QFDT) in its conventional interpretation? It is shown that the relation usually called as the QFDT is the condition of detailed macroscopic energetic balance. Following this interpretation the existing conflict between the two theorems in the quantum case is removed.

cond-mat.stat-mech↗

arXiv2002

Semiclassical theory of shot noise in ballistic n+-i-n+ semiconductor strucutres: relevance of Pauli and long range Coulomb correlations

We work out a semiclassical theory of shot noise in ballistic n+-i-n+ semiconductor structures aiming at studying two fundamental physical correlations coming from Pauli exclusion principle and long range Coulomb interaction. The theory provides a unifying scheme which, in addition to the current-voltage characteristics, describes the suppression of shot noise due to Pauli and Coulomb correlations in the whole range of system parameters and applied bias. The whole scenario is summarized by a phase diagram in the plane of two dimensionless variables related to the sample length and contact chemical potential. Here different regions of physical interest can be identified where only Coulomb or only Pauli correlations are active, or where both are present with different relevance. The predictions of the theory are proven to be fully corroborated by Monte Carlo simulations.

cond-mat.mes-hall↗

arXiv2002

A Percolative Model of Soft Breakdown in Ultrathin Oxides

The degradation of ultrathin oxide layers in the presence of a stress voltage is modeled in terms of two antagonist percolation processes taking place in a random resistor network. The resistance and leakage current fluctuations are studied by MonteCarlo simulations for voltages below the breakdown threshold. An increase of excess noise together with a noticeable non-Gaussian behavior is found in the pre-breakdown regime in agreement with experimental results.

cond-mat↗

arXiv2002

Resistance and Resistance Fluctuations in Random Resistor Networks Under Biased Percolation

We consider a two-dimensional random resistor network (RRN) in the presence of two competing biased percolations consisting of the breaking and recovering of elementary resistors. These two processes are driven by the joint effects of an electrical bias and of the heat exchange with a thermal bath. The electrical bias is set up by applying a constant voltage or, alternatively, a constant current. Monte Carlo simulations are performed to analyze the network evolution in the full range of bias values. Depending on the bias strength, electrical failure or steady state are achieved. Here we investigate the steady-state of the RRN focusing on the properties of the non-Ohmic regime. In constant voltage conditions, a scaling relation is found between $ / _0$ and $V/V_0$, where $ $ is the average network resistance, $ _0$ the linear regime resistance and $V_0$ the threshold value for the onset of nonlinearity. A similar relation is found in constant current conditions. The relative variance of resistance fluctuations also exhibits a strong nonlinearity whose properties are investigated. The power spectral density of resistance fluctuations presents a Lorentzian spectrum and the amplitude of fluctuations shows a significant non-Gaussian behavior in the pre-breakdown region. These results compare well with electrical breakdown measurements in thin films of composites and of other conducting materials.

cond-mat↗

arXiv2002

Linear and nonlinear regime of a Random Resistor Network under biased percolation

We investigate the steady state of a two-dimensional random resistor network subjected to two competing biased percolations as a function of the bias strength. The properties of the linear and nonlinear regimes are studied by means of Monte Carlo simulations. In constant current conditions, a scaling relation is found between $ / _0$ and $I/I_0$, where $ $ is the average network resistance, $ _0$ the Ohmic resistance and $I_0$ an appropriate threshold value for the onset of nonlinearity. A similar scaling relation is found also for the relative variance of resistance fluctuations. These results are in good agreement with electrical breakdown measurements performed in composite materials.

cond-mat.stat-mech↗

arXiv2001

Monte Carlo simulation of electromigration phenomena in metallic lines

The electromigration (EM) of metallic lines is studied in terms of competition between two percolative processes taking place in a random resistor network. The effects associated with the transport of mass and with the consequent growth of the internal stress are accounted for by stochastic generation and recovery of voids, driven by the external current. Monte Carlo simulations enable us to investigate within a unified theoretical framework a variety of relevant aspects of EM degradation as: damage patterns, the distribution of the time to failures, early stage resistance change in the presence of compositional effects, Black's law, geometrical effects, etc. A general agreement is found with the experimental findings.

cond-mat↗

arXiv2001

Stationary Regime of Random Resistor Networks Under Biased Percolation

The state of a 2-D random resistor network, resulting from the simultaneous evolutions of two competing biased percolations, is studied in a wide range of bias values. Monte Carlo simulations show that when the external current $I$ is below the threshold value for electrical breakdown, the network reaches a steady state with a nonlinear current-voltage characteristic. The properties of this nonlinear regime are investigated as a function of different model parameters. A scaling relation is found between $ / _0$ and $I/I_0$, where $ $ is the average resistance, $ _0$ the linear regime resistance and $I_0$ the threshold value for the onset of nonlinearity. The scaling exponent is found to be independent of the model parameters. A similar scaling behavior is also found for the relative variance of resistance fluctuations. These results compare well with resistance measurements in composite materials performed in the Joule regime up to breakdown.

cond-mat.stat-mech↗

arXiv2001

Fractional exclusion statistics and shot noise in ballistic conductors

We study the noise properties of ballistic conductors with carriers satisfying fractional exclusion statistics. To test directly the nature of exclusion statistics we found that systems under weakly degenerate conditions should be considered. Typical of these systems is that the chemical potential, $μ$ is in the thermal range $|μ|<3k_{B}T$. In these conditions the noise properties under current saturation are found to depend upon the statistical parameter $g$, displaying suppressed shot noise for $1/2\leq g\leq 1$, and enhanced shot noise for $0<g<1/2$, according to the attractive or repulsive nature of the carrier exclusion statistics.

cond-mat.str-el↗