A. O. Selskii

Effect of temperature on resonant electron transport through stochastic conduction channels in superlattices

We show that resonant electron transport in semiconductor superlattices with an applied electric and tilted magnetic field can, surprisingly, become more pronounced as the lattice and conduction electron temperature increases from 4.2 K to room temperature and beyond. It has previously been demonstrated that at certain critical field parameters, the semiclassical trajectories of electrons in the lowest miniband of the superlattice change abruptly from fully localized to completely unbounded. The unbounded electron orbits propagate through intricate web patterns, known as stochastic webs, in phase space, which act as conduction channels for the electrons and produce a series of resonant peaks in the electron drift velocity versus electric-field curves. Here, we show that increasing the lattice temperature strengthens these resonant peaks due to a subtle interplay between the thermal population of the conduction channels and transport along them. This enhances both the electron drift velocity and the influence of the stochastic webs on the current-voltage characteristics, which we calculate by making self-consistent solutions of the coupled electron transport and Poisson equations throughout the superlattice. These solutions reveal that increasing the temperature also transforms the collective electron dynamics by changing both the threshold voltage required for the onset of self-sustained current oscillations, produced by propagating charge domains, and the oscillation frequency.

Effect of interminiband tunneling on complex processes in a semiconductor superlattice

Spectra of current oscillations caused by the transport of the electron domains induced by an applied voltage in a semiconductor superlattice with the absence and presence of the tilted magnetic field are numerically investigated with allowance for the interband tunneling.

Effect of the form and localization of doping density perturbations on the current characteristics in a semiconductor superlattice

The effect doping density perturbations have on the current characteristics in a semiconductor superlattice is studied. The current characteristics are shown to depend on the localization and form of the perturbation. The effect of perturbations is strongest near the superlattice emitter. The effect grows along with the density profile integral and depends weakly on the form of the profile.

Space charge dynamics in a semiconductor superlattice affected by titled magnetic field and heating

The transition between different modes of current oscillations in a semiconductor superlattice, from close-to-harmonic (near the generation onset) to relaxation oscillations, has been investigated. The transition type is shown to change with an increase in temperature. A period-doubling bifurcation is observed at low temperatures. With an increase in temperature, the period-doubling bifurcation is observed at increasingly larger values of the voltage across the superlattice. The doubling bifurcation ceases to be observed at voltages at which the generation of oscillations of the current through the semiconductor superlattice is suppressed.

THz-generation in semiconductor superlattice in the external tilted magnetic field

We study effects of the external tilted magnetic field on the generation of sub-THz/THz oscillations in the semiconductor superlattice. We show that this field provides the increased power of harmonics in the THz range. Changing the tilt angle essentially influences the distribution of spectral power of current oscillations in the semiconductor superlattice.

Nonlinear correlation method for the separation of couplings in EEG experiments with neural ensembles

In the present paper the nonlinear association analysis of the EEG brain data in the process of bistable image perception are realized. Brain functional connectivity can be characterized by the temporal evolution of correlation between signals recorded from spatially-distributed regions. Numerous techniques were introduced for assessing this connectivity. Among nonlinear regression analysis methods, we chose a method introduced in the field of EEG analysis by Pijn, Lopes da Silva and colleagues, based on the fitting of a nonlinear curve by piecewise linear approximation, and more recently evaluated in a model of coupled neuronal populations. This method has some major advantages over other signal analysis methods such as coherence and cross-correlation functions because it can be applied independently of whether the type of relationship between the two signals is linear or nonlinear. In the capacity of bistable image we used a set of images based on a well-known bistable object, the Necker cube, as a visual stimulus. This is a cube with transparent faces and visible ribs. Bistability in perception consists in the interpretation of this 3D-object as to be oriented in two different ways, in particular, if the different ribs of the Necker cube are drawn with different intensity. It was shown that the structure of connections in the brain is different for cases without visual stimulation and with stimulation with the help of the Necker cube.

Synchronous regimes induced in semiconductor superlattices by a tilted magnetic field and external force

The effect a periodic electric field has on the dynamics of electron domains in a semiconductor superlattice with applied voltage and a magnetic field tilted relative to the superlattice axis is investigated. It is shown that this periodic electric field greatly affects the I–V characteristic of the superlattice and can induce several interesting phenomena, including the onset of synchronous regimes. The obtained results are compared to the data for a zero tilted magnetic field.

Model and software package for studying and optimizing generation characteristics of semiconductor superlattices

A software package for simulating the dynamics of semiconductor superlattices under the influence of an external magnetic field is developed. The analytical and numerical models on which the program package is based are described in detail in the paper. The approbation of the developed package shows that it can be effectively used to study the dynamics of semiconductor superlattices, including the optimization of the generation characteristics of subterahertz and terahertz devices.

Filtering as a way of varying the characteristics of intermittent behavior in two unidirectionally coupled tunnel diode generators

The intermittent behavior that can occur in chaotic systems upon signal filtering near the boundary of the chaotic phase synchronization regime is studied. It is found that in a system of unidirectionally coupled tunnel diode generators, it is possible for the eyelet and the ring intermittencies to exist simultaneously near the boundary of phase chaotic synchronization when a filter with certain parameters used.