Spin relaxation of localized electrons in n-type semiconductors

The mechanisms that determine spin relaxation times of localized electrons in impurity bands of n-type semiconductors are considered theoretically and compared with available experimental data. The relaxation time of the non-equilibrium angular momentum is shown to be limited either by hyperfine interaction, or by spin-orbit interaction in course of exchange-induced spin diffusion. The energy relaxation time in the spin system is governed by phonon-assisted hops within pairs of donors with an optimal distance of about 4 Bohr radii. The spin correlation time of the donor-bound electron is determined either by exchange interaction with other localized electrons, or by spin-flip scattering of free conduction-band electrons. A possibility of optical cooling of the spin system of localized electrons is discussed.Comment: Submitted to the special issue "Optical Orientation", Semiconductor Science and Technolog

Ultrafast control of donor-bound electron spins with single detuned optical pulses

The ability to control spins in semiconductors is important in a variety of fields including spintronics and quantum information processing. Due to the potentially fast dephasing times of spins in the solid state [1-3], spin control operating on the picosecond or faster timescale may be necessary. Such speeds, which are not possible to attain with standard electron spin resonance (ESR) techniques based on microwave sources, can be attained with broadband optical pulses. One promising ultrafast technique utilizes single broadband pulses detuned from resonance in a three-level Lambda system [4]. This attractive technique is robust against optical pulse imperfections and does not require a fixed optical reference phase. Here we demonstrate the principle of coherent manipulation of spins theoretically and experimentally. Using this technique, donor-bound electron spin rotations with single-pulse areas exceeding pi/4 and two-pulses areas exceeding pi/2 are demonstrated. We believe the maximum pulse areas attained do not reflect a fundamental limit of the technique and larger pulse areas could be achieved in other material systems. This technique has applications from basic solid-state ESR spectroscopy to arbitrary single-qubit rotations [4, 5] and bang-bang control[6] for quantum computation.Comment: 15 pages, 4 figures, submitted 12/2008. Since the submission of this work we have become aware of related work: J. Berezovsky, M. H. Mikkelsen, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom, Science 320: 349-352 (2008

Current Problems of Environmental Safety in the Republic of Tatarstan

Важным направлением в развивающемся мире является сохранение окружающей среды. Существует множество способом контроля и мониторинга состояния природы. В данной статье мы рассмотрим основные проблемы и методы обеспечения экологической безопасности в Республике Татарстан на примере таких городов как Набережные Челны, Альметьевск и Нижнекамск.An important direction in the developing world is the preservation of the environment. There are many ways to control and monitor the state of nature. In this article we will consider the main problems and methods of ensuring environmental safety in the Republic of Tatarstan on the example of cities such as Naberezhnye Chelny, Almetyevsk and Nizhnekamsk

Two-color picosecond and continuous-wave experiments on anti-Stokes and Stokes carrier-transfer phenomena in GaAslAl(x)Ga(1-x)As and InGaP2/AlxGa1-xAs heterostructures

We present direct evidence of the two-step absorption process in anti-Stokes photoluminescence in both GaAs/AlxGa1-xAs and InGaP2/AlxGa1-xAs heterostructures using two-color picosecond and continuous-wave photoluminescence experiments. We show information about the lifetime of the defect states that participate in the two-step absorption process. As a result, we conclude that the long-lived states rather than excitons play the dominant role in the two-step absorption process. We also study the possible contribution of the two-step absorption process to Stokes carrier transfer in GaAs/AlxGa1-xAs asymmetric double quantum well structuresclos

Strateginiai besivystančių šalių intelektinio potencialo ugdymo prioritetai kuriant novatorišką ekonomiką

The intellectual potential is considered as the fundamental basis for the innovative development of the industry and business entrepreneurship through influence factors. At the same time, there is no single clear definition of the term ‘intellectual potential’ and clearly developed organisational and economic mechanisms for its relationship with the trends of innovative development of the economic system. The purpose of the study is focused on the search for optimal and effective organisational and economic mechanisms for the development of the intellectual potential of countries with developing economies. The methodology was based on the application of the following scientific methods: analysis and synthesis, the statistical method of analysis, the method of establishing patterns and hypotheses, and the method of enlarged analytical calculation. Research and analysis of the main constituent elements and indicative data of the intellectual potential of developing countries of the world (the Republic of Kazakhstan and the Russian Federation) made it possible to identify systemic problems in this area. It can be concluded that the intellectual potential has significant reserves in the field of improvement and development, primarily in the field of human capital. As a result of the study, the authors propose ways of intensifying the development of intellectual potential on the principles of the formation of organisational and economic systems, such as creation and development of corporate-type universities; creation and development of regional and interregional competence centres; creation and development of business initiative centres

SPONTANEOUS DISSECTION OF CORONARY ARTERY AS A CAUSE OF ACUTE MYOCARDIAL INFARCTION

Spontaneous dissection of coronary arteries (SDCA) is a rare cause factor for acute myocardial infarction. The data provided is modern on the prevalence of SDCA, its predisposing factors as the data on diagnostics and treatment of SDCA. The case described of the myocardial infarction due to SDCA in 34-year old male