Solid-state physics and quantum electrodynamics, with its ultrarelativistic (massless) particles, meet in the electronic properties of one-dimensional carbon nanotubes, two-dimensional graphene or ...topological-insulator surfaces. However, clear experimental evidence for electronic states with a conical dispersion relation in all three dimensions, conceivable for certain bulk materials, is still missing. Here, we study a zinc-blende crystal, HgCdTe, at the point of the semiconductor-to-semimetal topological transition. For this compound, we observe three-dimensional massless electrons, as certified from the dynamical conductivity increasing linearly with the photon frequency, with a velocity of about 106 m s-1. Applying a magnetic field B results in a -dependence of dipole-active inter-Landau-level resonances and spin splitting of Landau levels also following a -dependence--well-established signatures of ultrarelativistic particles but until now not observed experimentally in any solid-state electronic system.
Searching for better materials for plasmonic and metamaterial applications is an inverse design problem where theoretical studies are necessary. Using basic models of impurity doping in ...semiconductors, transparent conducting oxides (TCOs) are identified as low-loss plasmonic materials in the near-infrared wavelength range. A more sophisticated theoretical study would help not only to improve the properties of TCOs but also to design further lower-loss materials. In this study, optical functions of one such TCO, gallium-doped zinc oxide (GZO), are studied both experimentally and by first-principles density-functional calculations. Pulsed-laser-deposited GZO films are studied by the x-ray diffraction and generalized spectroscopic ellipsometry. Theoretical studies are performed by the total-energy-minimization method for the equilibrium atomic structure of GZO and random phase approximation with the quasiparticle gap correction. Plasma excitation effects are also included for optical functions. This study identifies mechanisms other than doping, such as alloying effects, that significantly influence the optical properties of GZO films. It also indicates that ultraheavy Ga doping of ZnO results in a new alloy material, rather than just degenerately doped ZnO. This work is the first step to achieve a fundamental understanding of the connection between material, structural, and optical properties of highly doped TCOs to tailor those materials for various plasmonic applications.
Nanophotonic devices offer an unprecedented ability to concentrate light into small volumes which can greatly increase nonlinear effects. However, traditional plasmonic materials suffer from low ...damage thresholds and are not compatible with standard semiconductor technology. Here we study the nonlinear optical properties in the novel refractory plasmonic material titanium nitride using the Z-scan method at 1550 nm and 780 nm. We compare the extracted nonlinear parameters for TiN with previous works on noble metals and note a similarly large nonlinear optical response. However, TiN films have been shown to exhibit a damage threshold up to an order of magnitude higher than gold films of a similar thickness, while also being robust, cost-efficient, bio- and CMOS-compatible. Together, these properties make TiN a promising material for metal-based nonlinear optics.
An epitaxial layer of HgCdTe-a THz detector-was studied in magnetotransmission, magnetoconductivity and magnetophotoconductivity experiments at cryogenic temperatures. In the optical measurements, ...monochromatic excitation with photon frequency ranging from 0.05 THz to 2.5 THz was used. We show a resonant response of the detector at magnetic fields as small as 10 mT with the width of the resonant line equal to about 5 mT. Application of a circular polarizer at 2.5 THz measurements allowed for confirming selection rules predicted by the theory of optical transitions in a narrow-gap semiconductor and to estimate the band-gap to be equal to about 4.5 meV. The magnetoconductivity tensor was determined as a function of magnetic field and temperature 2 K <
< 120 K and analysed with a standard one-carrier conductivity model and the mobility spectrum technique. The sample showed n-type conductivity at all temperatures. At temperatures above about 30 K, conductivity was found to be reasonably described by the one-carrier model. At lower temperatures, this description is not accurate. The algorithm of the spectrum of mobility applied to data measured below 30 K showed presence of three types of carriers which were tentatively interpreted as electrons, light holes and heavy holes. The mobility of electrons and light holes is of the order of 10 6 cm 2 /Vs at the lowest temperatures. Magnetophotoconductivity experiments allowed for proposing a detector working at 2 K and 50 mT with a flat response between 0.05 THz and 2.5 THz.
Electron wave functions in the conduction band of zero-gap HgCdTe alloy are calculated in the Coulomb acceptor field. The resonant-state energies are determined.
Two waveguide heterostructures with an array of 10 HgCdTe/CdHgTe quantum wells grown within a single technological series and designed to generate stimulated emission near 20 and 30 μm are studied. ...At a temperature of 10 K, stimulated emission in the “short-wavelength” structure is obtained at a wavelength of ∼23.9 μm, while in the “long-wavelength” structure stimulated emission is not observed. Calculations of optical absorption in the passive layers for both structures are carried out and it is demonstrated that its level is higher in the long-wavelength structure. Approaches are proposed to minimize its effect on the generation of stimulated emission.
Comparative studies (gel permeation chromatography and evaluation of turbulent drag reduction effectiveness on a turbulence rheometer) of ultra-high molecular weight polymers from a series of higher ...alpha-olefins (hexene, octene, decene, dodecene) used as hydrodynamic drag agents have been carried out. It was found that the activity of hexene in the polymerization on a titanium magnesium catalyst, if all other relevant factors remain unaltered, significantly exceeds the activity of octene, decene, and dodecene (the conversion of hexene in 24 h is almost 1.5 times higher than the conversion of other monomers over the same time), and the rates of polymerization of the latter differ slightly. The average molecular weights of all polymers differ only slightly: ~6 millions Da for polyhexene and ~5 millions Da for all the others. At the same time, the drag reduction effectiveness of the polymers showed a significant dependence on the nature of the initial monomers: the drag reduction effectiveness rapidly diminishes with an increase in the molecular weight of the corresponding alpha-olefin (3–4 times upon transition from polyhexene to polydodecene).
Data on the synthesis of structures for a quantum cascade terahertz laser in the AlGaAs/GaAs material system on GaAs substrates using the molecular-beam-epitaxy method and their characterization are ...presented. The specific features necessary for the implementation of such structures are considered. It is shown that, for this configuration, almost single-mode lasing is observed at a frequency of
~
3 THz up to a temperature of ~60 K.
Heterostructures with thin Hg(Cd)Te/CdHgTe quantum wells (QWs) are attractive for the development of mid-infrared interband lasers. Of particular interest are room-temperature operating emitters for ...the short-wavelength infrared range (SWIR, typically defined as 1.7–3 μm). In this work, we report on the observation of stimulated emission (SE) in the 2.65–2.75 µm wavelength range at room temperature in an optically pumped HgCdTe QW laser heterostructure. We study a series of three samples with lengths ranging from 2.5 to 7 mm and discuss the effects related to the non-uniformity of the excitation beam profile. SE threshold intensity and the magnitude of pump-induced carrier heating are found to be effectively dependent on the chip size, which should be accounted for in possible designs of HgCdTe-based optical converters. We also pay attention to the problem of active medium engineering in order to push the SE wavelength towards the 3–5 µm atmospheric window and to lower the SE threshold.
The urgency of the studied issue is due to the fact that the single agricultural tax (SAT) is an advantageous taxation system: there is one tax that replaces several other taxes, due to which the ...burden on business is significantly reduced. The purpose of the article is to solve the task of developing a system of state support for the agro-industrial complex of Russia in the direction of developing effective approaches to the taxation of agricultural producers. The practice of applying SAT and managing its further improvement is controversial, but the need for further economic and tax incentives for business entities in the agricultural sector is obvious. In the process of research, important theoretical and practical results were obtained. On the basis of the analysis of existing mechanisms in the agro-industrial complex, areas requiring scientific and methodological comprehension were identified: risks in agriculture, the specifics of financial relations, the level of tax burden, the relevance of the application of differentiated approaches to taxation. The paper outlines the role of the state as the main regulator of the agro-industrial complex in the process of implementing the national policy on food security. The paper identifies the characteristics of the tax base and SAT accruals in Russia in 2007-2016, analyzes the modern practice of SAT application by agricultural producers of Russia, investigates the advantages and disadvantages of SAT, the problematic aspects of SAT The study presents conceptually new methodological approaches for the further development of SAT. The practical significance of the study lies in the possibility of using its materials and results by the Ministry of Finance of the Russian Federation and the Federal Tax Service for the purposes of tax planning and forecasting the amount of tax revenues from organizations belonging to the agro-industrial complex; by the Ministry of Agriculture of the Russian Federation for the purpose of studying the optimal combination of a set of instruments of state financial support for the agro-industrial complex, distribution of subsidies and tax burden on its subjects. The results of the research can be used to prepare educational materials for the disciplines: "Taxes and the tax system of the Russian Federation", "Taxation of organizations", etc.
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