High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

ABOUT DYNAMICS OF THE GEOPOLITICAL POSITION OF THE NORTH-EAST OF RUSSIA IN THE 17-TH-21-ST CENTURIES

Purpose: In the article, the changes in the geopolitical situation on the North-East for four preceding, partial centuries are considered. Methodology: Up to the inclusion in the structure of Russia, this extensive region (2.3 million km2) with the considerable natural-resources potential has actually existed out of the world geopolitical processes, basically, because of the extremeness of the natural climatic conditions, remoteness from the centers of world civilization and limited technical and technological capabilities in those times. Result: The different stages in the state of the geopolitical position of the region in prior centuries are identified and their repeatedly and multidirectional varying characteristics during the period in question are reported. It is also emphasized that the measures attempted by Russia for strengthening of the geopolitical position on the North-East gave rise abroad to the negative response consonant with the current ones practically at all considered stages. The current stage is considered as a period of the drastically varying external geopolitical conditions and increased technical capabilities when the geopolitical significance of the North-East for Russia increases by a factor of many times. Applications: This research can be used for universities, teachers, and students. Novelty/Originality: In this research, the model of About Dynamics of the Geopolitical Position of the North-East of Russia in the 17-th-21-st Centuries is presented in a comprehensive and complete manner

Theoretical backgrounds of nonlinear THz spectroscopy of semiconductor superlattices

We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.Comment: 14 page

Negative high-frequency differential conductivity in semiconductor superlattices

We examine the high-frequency differential conductivity response properties of semiconductor superlattices having various miniband dispersion laws. Our analysis shows that the anharmonicity of Bloch oscillations (beyond tight-binding approximation) leads to the occurrence of negative high-frequency differential conductivity at frequency multiples of the Bloch frequency. This effect can arise even in regions of positive static differential conductivity. The influence of strong electron scattering by optic phonons is analyzed. We propose an optimal superlattice miniband dispersion law to achieve high-frequency field amplification