Elastic Spin Relaxation Processes in Semiconductor Quantum Dots

Electron spin decoherence caused by elastic spin-phonon processes is investigated comprehensively in a zero-dimensional environment. Specifically, a theoretical treatment is developed for the processes associated with the fluctuations in the phonon potential as well as in the electron procession frequency through the spin-orbit and hyperfine interactions in the semiconductor quantum dots. The analysis identifies the conditions (magnetic field, temperature, etc.) in which the elastic spin-phonon processes can dominate over the inelastic counterparts with the electron spin-flip transitions. Particularly, the calculation results illustrate the potential significance of an elastic decoherence mechanism originating from the intervalley transitions in semiconductor quantum dots with multiple equivalent energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity and phonon decay in spin relaxation is also examined along with that of the local effective field fluctuations caused by the stochastic electronic transitions between the orbital states. Numerical estimations are provided for typical GaAs and Si-based quantum dots.Comment: 57 pages, 14 figure

Thermally Activated Resonant Magnetization Tunneling in Molecular Magnets: Mn_12Ac and others

The dynamical theory of thermally activated resonant magnetization tunneling in uniaxially anisotropic magnetic molecules such as Mn_12Ac (S=10) is developed.The observed slow dynamics of the system is described by master equations for the populations of spin levels.The latter are obtained by the adiabatic elimination of fast degrees of freedom from the density matrix equation with the help of the perturbation theory developed earlier for the tunneling level splitting [D. A. Garanin, J. Phys. A, 24, L61 (1991)]. There exists a temperature range (thermally activated tunneling) where the escape rate follows the Arrhenius law, but has a nonmonotonic dependence on the bias field due to tunneling at the top of the barrier. At lower temperatures this regime crosses over to the non-Arrhenius law (thermally assisted tunneling). The transition between the two regimes can be first or second order, depending on the transverse field, which can be tested in experiments. In both regimes the resonant maxima of the rate occur when spin levels in the two potential wells match at certain field values. In the thermally activated regime at low dissipation each resonance has a multitower self-similar structure with progressively narrowing peaks mounting on top of each other.Comment: 18 pages, 8 figure

Влияние адаптогена аскорбата лития на микробиоту рубца овец-ярок

Health and productivity of ruminants directly depend on the state of rumen and digestion in intestinal tract. Normal microflora protects the body from pathogenic microbes, stimulates the immune system, participates in metabolic reactions and plays an important role in energy metabolism. Disturbance of species composition of microflora in rumen under effect of various factors leads to a state of dysbiosis, disorders of products digestibility, changes in enzymatic processes and other disorders. Biologically active substances of an adaptogenic nature can show immunomodulatory and antimicrobial activity. Adaptogen lithium ascorbate has stress-protective, neurotrophic, neuroprotective, antioxidant, immunomodulatory properties. In this paper, using molecular genetic methods, the effect of lithium ascorbate on composition of rumen microbiota of sheep was studied for the first time.  Composition of microbiota was determined by NGS sequencing method. In total, 37 phylums, 76 classes, 98 orders, 225 families and 894 species of microorganisms were identified. It has been determined that introduction of lithium ascorbate at a dose of 10 mg/kg of body weight into the main diet of sheep contributed to increase in proportion of cellulolytic bacteria from 73.6±1.6% to 75.4±0.9% and over 40% decrease in total number of infusoria in rumen content. Cellulolytic activity of rumen fluid in sheep of the experimental group increased by 38% compared to the animals of the control group. The number of pathogenic bacteria decreased from 2.7% in sheep of the control group to 1.6% in animals of the experimental group, while the content of beneficial bacilli increased from 0.3% to 0.5%, respectively. Content of undesirable and conditionally pathogenic microflora decreased in the sheep of experimental group. The obtained data confirm positive effect of adaptogen lithium ascorbate, introduced into diet at a dosage of 10 mg/kg of body weight, on qualitative and quantitative composition of microbiota in sheep rumen. Therefore, lithium ascorbate, a broad-spectrum adaptogen, can be recommended as a feed additive to the main diet of sheep to improve rumen digestion and increase productivity.Здоровье и продуктивность жвачных животных напрямую зависят от рубцового и кишечного пищеварения. Нормальная микрофлора защищает организм от патогенных микробов, стимулирует иммунную систему, участвует в метаболических реакциях и играет важную роль в энергетическом обмене. Нарушение видового состава микрофлоры рубца под влиянием различных факторов приводит к изменению усвояемости продуктов пищеварения, изменениям ферментативных процессов и развитию прочих патологических процессов. Биологически активные вещества адаптогенной природы могут проявлять иммуномодулирующую и антимикробную активность. Адаптоген аскорбат лития обладает стресс-протекторными, нейротрофическими, нейропротекторными, антиоксидантными, иммуномодулирующими свойствами и в качестве кормовой добавки влияет на микробиоту рубца. В настоящем исследовании при использовании NGS-секвенирования впервые изучено влияние адаптогена аскорбата лития на бактериальное сообщество рубца овец-ярок романовской породы. На фоне длительного содержания овец на основном рационе в условиях вивария ВНИИФБиП нормофлора рубца не подвергалась негативным изменениям. Введение органической соли лития в состав основного рациона в дозировке 10 мг/кг живой массы способствовало усилению процессов ферментации в рубце, достоверному росту целлюлозолитической активности, снижению суммарной доли патогенных и доли некоторых условно-патогенных микроорганизмов в рубцовом содержимом. Полученные данные свидетельствуют о благотворном влиянии введения аскорбата лития в качестве добавки к основному рациону на состав микробиоты рубца овец

Anisotropic properties of spin avalanches in crystals of nanomagnets

Anisotropy effects for spin avalanches in crystals of nanomagnets are studied theoretically with the external magnetic field applied at an arbitrary angle to the easy axis. Starting with the Hamiltonian for a single nanomagnet in the crystal, two essential quantities characterizing spin avalanches are calculated: the activation and Zeeman energies. The calculation is performed numerically for a wide range of angles and analytical formulas are derived within the limit of small angles. The anisotropic properties of a single nanomagnet lead to anisotropic behavior of the magnetic deflagration speed. Modifications of the magnetic deflagration speed are investigated for different angles between the external magnetic field and the easy axis of the crystals. Anisotropic properties of magnetic detonation are also studied, which concern, first of all, the temperature behind the leading shock and the characteristic time of spin switching in the detonation

Experimental evidence of the role of quasilocalized phonons in the thermal conductivity of simple alcohols in orientationally ordered crystalline phases

The thermal conductivity к(T) of crystalline alcohols (methyl, ethyl and 1-propyl) within their thermodynamic equilibrium phases for T ≥ 2 K and under the equilibrium vapor pressures has been measured and analyzed. While such compounds usually exhibit a rich polymorphism including amorphous and partially ordered crystals, the phases here explored correspond to crystals showing complete orientational order. The results show that the temperature dependence of к(T) above its maximum deviates from the expected decrease following a 1/T law with increasing temperature arising from anharmonic interactions involving acoustic excitations. Such a deviation is here attributed to the presence of a component кII(T) corresponding to the shortest-lifetime phonons (Cahill–Pohl model) additional to that кI(T) related to propagating phonons and thus: к(T) = кI(T) + кII(T). Above T = 40 K кI(T) does follow the law 1/T and кII(T) is basically temperature independent. The component кI(T) is well described by the Debye–Peierls model taking into account the phonon–phonon Umklapp processes and phonon scattering by dislocations. In turn, the contribution кII(T) is attributed to the effects of higher lying excitations which get thermally populated above some 40 K. Finally, a systematic trend is found concerning the strength of phonon–phonon scattering which is seen to diminish as the number of carbon atoms in the alcohol molecule increases