Narrow Results

The Rashba spin–orbit coupling (RSOC) effect on the polarization and shot noise properties in a strained WSe₂ multiple barrier structure is studied by transfer-matrix technique. The results indicate that the spin-dependent Fano factor depends on the strain and RSOC strength with oscillatory evolution. Thus, the value of Fano factor with spin rotation can be tuned mechanically and by an external electric field. Also, Fano factor shows high sensitivity to the number of electrostatic barriers in strained WSe₂ multiple barrier structure. Meanwhile, in a strained WSe₂ multiple barrier structure both sign and value of the valley and spin polarizations could be adjusted by tuning both RSOC and strain strength. These findings show that a WSe₂ multiple barrier structure under strain and RSOC can be useful for future spintronics, straintronic and valleytronic devices.

We investigated the spin-dependent shot noise in aperiodic semiconductor multilayers heterostructures in the presence of the Rashba spin-orbit interaction and an electric field. The results indicate that the shot noise and Fano factor are strongly spin-dependent and can be greatly modulated not only by the external bias voltage and Rashba spin-orbit interaction but also by the thicknesses of block A and B. Our investigations may provide away to design the detection system electronic devices.

In this paper, we theoretically study the ballistic transport through a weakly open circular mesostructure within the framework of pseudopath semiclassical approximation. By defining the interference factor and comparing it numerically with the transmission amplitude, we demonstrate that the fluctuations in transmission amplitude are mainly due to the interference effects between different classical trajectories. In addition, we calculate the Fano factor versus cutoff length of classical trajectories in the energy domain to illustrate that the fluctuations in transmission amplitude mainly arise from the contribution of short-length classical trajectories. We further show that the transmission length power spectra not only associate with a lot of classical trajectories but with a series of nonclassical trajectories due to the diffraction scattering effects. Moreover, we show that the classical trajectories distributed in the mode–mode coupling function give the largest contribution to the corresponding transmission amplitude. We hope that our results and analysis can be used to reveal new effects of mesoscopic systems and to provide theoretical basis for the design of mesoscopic devices.

The effects of carrying capacity of environment $K$ for degradation (the $K$ effect for short) on the constitutive gene expression and a simple genetic regulation system are investigated by employing a stochastic Langevin equation combined with the corresponding Fokker–Planck equation for the two stochastic systems subjected to internal and external noises. This $K$ effect characterizes the limited degradation ability of the environment for RNA or proteins, such as insufficient catabolic enzymes. The $K$ effect could significantly change the distribution of mRNA copy-number in constitutive gene expression, and interestingly, it leads to the Fano factor slightly larger than one if only the internal noise exists. Therefore, that the recent experimental measurements suggest the Fano factor deviates from one slightly [D. L. Jones, R. C. Brewster and R. Phillips, Science346 (2014) 1533], probably originates from the $K$ effect. The $K$ effects on the steady and transient properties of genetic regulation system, have been investigated in detail. It could enhance the mean first passage time significantly especially when the noises are weak and reduce the signal-to-noise ratio in stochastic resonance substantially.

The Andreev conductance in $\mathrm{\Delta }$-shaped quantum dots (QDs) system coupled with Majorana bound states (MBSs) is studied and resulting conductance spectrum displays resonant and non-resonant processes. These fluctuated resonances render features like insulating band, bonding (antibonding) in the low-bias region due to non-trivial role of interdot coupling $t_c$ and dots-MBSs coupling $\lambda$. On comparing QD levels $({𝜀}_1,{𝜀}_2,{𝜀}_3)$, and the coupling between the MBSs, coherent oscillating dynamics of an electron between the nanowire and the QDs can be portrayed. The insulating band is robust against $\lambda$, but highly sensitive to $t_c$, which causes to increase (decrease) the conductance. We can claim that under finite bias voltage, transport can facilitate the researchers to expose the essential features of the Majorana fermion in such closed systems composed of MBSs.

We investigate the time dynamics of sequences of earthquakes occurred in three different seismic zones in Italy. All the series analyzed present 1/f^α temporal fluctuations, shown by the power-law behaviour of several statistics (Fano Factor, Allan Factor and Count-based Periodogram), that allow to detect correlation properties in point processes.

Point processes, like other geophysical phenomena, such as earthquakes or avalanches, are well suited to model rain event sequences. Time-clustering analysis has been performed over rainfall sequences by using the statistical approaches of Fano Factor and Allan Factor. The obtained results suggest the presence of clustering in the time distribution of the sequence of rain events, with scaling exponent α ranging between ~0.35 and ~0.42.

Intentionally designed silicon microplasmas with breakdown voltage 10.4–10.8 V have been investigated. Avalanche pulse rate time dependence and Fano factor were measured to evidence the presence of time-clustering in the series of pulses. The two-level fluctuations of avalanche pulse rate were observed for diodes containing two charge multiplication regions. Probabilistic model for pulse rate fluctuations was introduced.

The temporal fluctuations of the 1880–1994 seismicity recorded in Pannonian Basin were investigated by means of the Fano Factor and Allan Factor methods, which allows us to estimate the power spectrum for point processes. Up to our knowledge, this is the first scaling analysis performed on earthquake series spanning for almost one century. Our findings point out a presence of two temporal regimes in the analyzed seismicity, which is characterized by quasi-Poissonian behavior for low to intermediate timescales for up to about 1/2 years, and by scaling behavior for higher timescales with scaling exponent around 0.3–0.4, indicating a rather high time-clustering of the events. Furthermore the Allan Factor shows the presence of a periodicity at about 2.23 years for events with magnitude larger or equal to 3.5.

We discuss the possibility of diffusive conduction and thus of suppression of shot noise by a factor 1/3 in mesoscopic semiconductor devices with two-dimensional and one-dimensional potential disorder, for which existing experimental data do not provide a conclusive result. On the basis of our numerical analysis, we conclude that it is quite difficult to achieve diffusive transport over a reasonably wide parameter range, unless the device dimensions are increased up to the macroscopic scale where, however, shot noise disappears because the device length exceeds the Debye length. In addition, in the case of one-dimensional disorder, some mechanism capable of mode-mixing has to be present in order to reach or even approach the diffusive regime.

Quantum transport properties through some multilevel quantum dots sandwiched between two metallic contacts are investigated by the use of Green's function technique. Here, we do parametric calculations, based on the tight-binding model, to study the transport properties through such bridge systems. The electron transport properties are significantly influenced by (a) the number of quantized energy levels in the dots, (b) the dot-to-electrodes coupling strength, (c) the location of the equilibrium Fermi energy E_F, and (d) the surface disorder. In the limit of weak-coupling, the conductance (g) shows sharp resonance peaks associated with the quantized energy levels in the dots, while, they get substantial broadening in the strong-coupling limit. The behavior of the electron transfer through these systems becomes much more clearly visible from our study of the current–voltage (I–V) characteristics. In this context, we also describe the noise power of current fluctuations (S) and determine the Fano factor (F) which provides an important information about the electron correlation among the charge carriers. Finally, we explore a novel transport phenomenon by studying the surface disorder effect in which the current amplitude increases with the increase of the surface disorder strength in the strong disorder regime, while, the amplitude decreases in the limit of weak disorder. Such an anomalous behavior is completely opposite to that of bulk disordered system where the current amplitude always decreases with the disorder strength. It is also observed that the current amplitude strongly depends on the system size which reveals the finite quantum size effect.

We discuss the possibility of diffusive conduction and thus of suppression of shot noise by a factor 1/3 in mesoscopic semiconductor devices with two-dimensional and one-dimensional potential disorder, for which existing experimental data do not provide a conclusive result. On the basis of our numerical analysis, we conclude that it is quite difficult to achieve diffusive transport over a reasonably wide parameter range, unless the device dimensions are increased up to the macroscopic scale where, however, shot noise disappears because the device length exceeds the Debye length. In addition, in the case of one-dimensional disorder, some mechanism capable of mode-mixing has to be present in order to reach or even approach the diffusive regime.