Cubic anisotropy of hole Zeeman splitting in semiconductor nanocrystals

We study theoretically cubic anisotropy of Zeeman splitting of a hole localized in semiconductor nanocrystal. This anisotropy originates from three contributions: crystallographic cubically-symmetric spin and kinetic energy terms in the bulk Luttinger Hamiltonian and the spatial wave function distribution in a cube-shaped nanocrystal. From symmetry considerations, an effective Zeeman Hamiltonian for the hole lowest even state is introduced, containing a spherically symmetric and a cubically symmetric term. The values of these terms are calculated numerically for spherical and cube-shaped nanocrystals as functions of the Luttinger Hamiltonian parameters. We demonstrate that the cubic shape of the nanocrystal and the cubic anisotropy of hole kinetic energy (so called valence band warping) significantly affect effective $g$ factors of hole states. In both cases, the effect comes from the cubic symmetry of the hole wave functions in zero magnetic field. Estimations for the effective $g$ factor values in several semiconductors with zinc-blende crystal lattices are made. Possible experimental manifestations and potential methods of measurement of the cubic anisotropy of the hole Zeeman splitting are suggested.Comment: 17 pages, 7 figure

Surface spin magnetism controls the polarized exciton emission from CdSe nanoplatelets

The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetism owing to the uncompensated spins of dangling bonds (DBSs). We reveal that by optical spectroscopy in high magnetic fields up to 15 Tesla using the exciton spin as probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the DBS and exciton spin polarization as well as by the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction can be adjusted by the nanoplatelet growth conditions

Electron and hole g-factors and spin dynamics of negatively charged excitons in CdSe/CdS colloidal nanoplatelets with thick shells

We address spin properties and spin dynamics of carriers and charged excitons in CdSe/CdS colloidal nanoplatelets with thick shells. Magneto-optical studies are performed by time-resolved and polarization-resolved photoluminescence, spin-flip Raman scattering and picosecond pump-probe Faraday rotation in magnetic fields up to 30 T. We show that at low temperatures the nanoplatelets are negatively charged so that their photoluminescence is dominated by radiative recombination of negatively charged excitons (trions). Electron g-factor of 1.68 is measured and heavy-hole g-factor varying with increasing magnetic field from -0.4 to -0.7 is evaluated. Hole g-factors for two-dimensional structures are calculated for various hole confining potentials for cubic- and wurtzite lattice in CdSe core. These calculations are extended for various quantum dots and nanoplatelets based on II-VI semiconductors. We developed a magneto-optical technique for the quantitative evaluation of the nanoplatelets orientation in ensemble

Addressing the exciton fine structure in colloidal nanocrystals: the case of CdSe nanoplatelets

We study the band-edge exciton fine structure and in particular its bright-dark splitting in colloidal semiconductor nanocrystals by four different optical methods based on fluorescence line narrowing and time-resolved measurements at various temperatures down to 2 K. We demonstrate that all these methods provide consistent splitting values and discuss their advances and limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5 monolayers are chosen for experimental demonstrations. The bright-dark splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional to the nanoplatelet thickness. Good agreement between experimental and theoretically calculated size dependence of the bright-dark exciton slitting is achieved. The recombination rates of the bright and dark excitons and the bright to dark relaxation rate are measured by time-resolved techniques

Experimental definition of speed of cumulative flow progress through destructable obstacle

Головатенко Владислав Денисович. Заслуженный конструктор Российской Федерации, ведущий инженер-конструктор, ОАО «ОКБ «Новатор» (Екатеринбург), [email protected]. Головатенко Андрей Владиславович. Консультант-сотрудник, ОАО «ОКБ «Новатор» (Санкт-Петербург), [email protected]. V.D. Golovatenko, EMDB “Novator”. LLC, Yekaterinburg, Russian Federation, [email protected], A.V. Golovatenko, EMDB “Novator”. LLC, S. Petersburg, Russian Federation, [email protected]Описан метод определения скорости прохождения кумулятивной струи непосредственно в преграде. Найдено, что эта осреднённая во времени скорость меньше скорости детонации взрывчатого вещества, на порядок уступает скорости прохождения звука в металле преграды и меньше скорости перемещения продуктов детонации. Результаты экспериментов коррелируют с вязкоупругой моделью разрушения преграды кумулятивной струёй. A method is described to define the speed of advance of cumulative flow directly in an obstacle. It is found out that this speed, if averaged in time, is less than the speed of explosive detonation, is about ten times less than the sound speed in metal and less than the speed of movement oа detonation products. These results prove the viscouselastic model of obstacle destruction by a cumulative flow

Process of interaction of hollow charge stream with a barrier

Головатенко Владислав Денисович. Заслуженный конструктор Российской Федерации, ведущий инженер-конструктор ОАО «ОКБ „Новатор“», г. Екатеринбург. Область научных интересов – исследование импульсных процессов, протекающих при горении топлив в устройствах малой мощности систем автоматизации летательных аппаратов. Тел.: (343) 264-64-16. Vladislav D. Golovatenko. The honored designer of the Russian Federation, the principal designer of EMDB “Novator”, Yekaterinburg. The area of scientific interests – the analysis of impulse processes, running in low capacity mechanisms of automation systems during fuel-burn. Tel.: (343) 264-64-16. Головатенко Андрей Владиславович. Консультант ОАО «ОКБ „Новатор“», г. Санкт-Петербург. Область научных интересов – методологические вопросы общей физики. Andrey V. Golovatenko. Сonsulting engineer of EMDB “Novator”, St. Petersburg. The area of scientific interests – metrological issues of general physics.В настоящей работе рассматриваются физическая модель взаимодействия кумулятивного тела с преградой, которая может быть описана уравнениями в частных производных, а также способы управления движением кумулятивной струи. Кумулятивная струя представлена как вязкоупругое тело. Определено, что кумуляция включает этапы сжатия металлического вкладыша заряда, ударное и тепловое воздействие струи на преграду, вымывания продуктов разрушения из каверны. The current work deals with a physical model of interaction of hollow charge stream with a barrier described using particular derivatives equations, as well as the methods of hollow charge stream control. Hollow charge stream is presented as viscous-elastic body. It is proved that that the stream forming includes compressing the charge internal metal impact and thermal action of a stream against a barriers, and withdrawal of destructtion products from a cavern.ОКБ „Новатор