Impurity-enhanced Aharonov-Bohm effect in neutral quantum-ring magnetoexcitons

We study the role of impurity scattering on the photoluminescence (PL) emission of polarized magnetoexcitons. We consider systems where both the electron and hole are confined on a ring structure (quantum rings) as well as on a type-II quantum dot. Despite their neutral character, excitons exhibit strong modulation of energy and oscillator strength in the presence of magnetic fields. Scattering impurities enhance the PL intensity on otherwise "dark" magnetic field windows and non-zero PL emission appears for a wide magnetic field range even at zero temperature. For higher temperatures, impurity-induced anticrossings on the excitonic spectrum lead to unexpected peaks and valleys on the PL intensity as function of magnetic field. Such behavior is absent on ideal systems and can account for prominent features in recent experimental results.Comment: 7 pages, 7 figures, RevTe

Magnetoexcitons in quantum-ring structures: a novel magnetic interference effect

A novel magnetic interference effect is proposed for a neutral, but polarizable exciton in a quantum ring with a finite width. The magnetic interference effect originates from the nonzero dipole moment in the exciton. The ground state of exciton acquires a nonzero angular momentum with increasing normal magnetic field. This leads to the suppression of the photoluminescence in defined windows of the magnetic field.Comment: 6 pages, 2 figures, Proceed. EP2DS, 2001 (Physica E

Solution of the Schr\"odinger Equation for Quantum Dot Lattices with Coulomb Interaction between the Dots

The Schr\"odinger equation for quantum dot lattices with non-cubic, non-Bravais lattices built up from elliptical dots is investigated. The Coulomb interaction between the dots is considered in dipole approximation. Then only the center of mass (c.m.) coordinates of different dots couple with each other. This c.m. subsystem can be solved exactly and provides magneto- phonon like collective excitations. The inter-dot interaction is involved only through a single interaction parameter. The relative coordinates of individual dots form decoupled subsystems giving rise to intra-dot excitations. As an example, the latter are calculated exactly for two-electron dots. Emphasis is layed on qualitative effects like: i) Influence of the magnetic field on the lattice instability due to inter-dot interaction, ii) Closing of the gap between the lower and the upper c.m. mode at B=0 for elliptical dots due to dot interaction, and iii) Kinks in the single dot excitation energies (versus magnetic field) due to change of ground state angular momentum. It is shown that for obtaining striking qualitative effects one should go beyond simple cubic lattices with spherical dots. We also prove a more general version of the Kohn Theorem for quantum dot lattices. It is shown that for observing effects of electron- electron interaction between the dots in FIR spectra (breaking Kohn's Theorem) one has to consider dot lattices with at least two dot species with different confinement tensors.Comment: 11 figures included as ps-file

Excitons in quantum-ring structures in a magnetic field: Optical properties and persistent currents

We study theoretically the magnetic field effect on a neutral, but polarizable exciton confined in quantum-ring structures. For excitons with a nonzero dipole moment, a novel magnetic interference effect occurs: The ground state of an exciton confined in a finite-width quantum ring possesses a nonzero angular momentum with increasing normal magnetic field. This effect is accompanied by a suppression of the photoluminescence in well-defined magnetic-field intervals. The magnetic interference effect is calculated for type-II quantum dots and quantum rings.Comment: 10 pages, 2 figures, Proceed. MSS-10, 2001 (Physica E

Molecular spintronics: Coherent spin transfer in coupled quantum dots

Time-resolved Faraday rotation has recently demonstrated coherent transfer of electron spin between quantum dots coupled by conjugated molecules. Using a transfer Hamiltonian ansatz for the coupled quantum dots, we calculate the Faraday rotation signal as a function of the probe frequency in a pump-probe setup using neutral quantum dots. Additionally, we study the signal of one spin-polarized excess electron in the coupled dots. We show that, in both cases, the Faraday rotation angle is determined by the spin transfer probabilities and the Heisenberg spin exchange energy. By comparison of our results with experimental data, we find that the transfer matrix element for electrons in the conduction band is of order 0.08 eV and the spin transfer probabilities are of order 10%.Comment: 13 pages, 6 figures; minor change

Unbound states in quantum heterostructures

We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron – hole states. The part played by Auger scattering in Quantum Dots is also discussed

Брахиметакарпия: особенности патологии и ее оперативного лечения

The purpose - to study the morphofunctional changes of upper extremities in patients with brachymetacarpia. Material and methods. The results of the examination and surgical treatment by distraction osteosynthesis of six patients (10 hands, shortening of the 18-metacarpal bones) with brachymetacarpia are presented. Results. All patients noted dissatisfaction with the cosmetic state of hands and tiredness during physical activities with the hand. IV ray was shortened in 50%, V ray - in 33% of cases and III ray - in 17%. Limitation of active flexion was noted in all patients, an average flexion was 58.9 ± 7,1°. After treatment flexion increased an average on 20.5 ° (22.7%). Complications were obtained in two patients on three hands. Conclusions. Brachymetacarpia is a rare disease, the etiology of which is still unknown and requires further study. In all cases of brachymetacarpia there is a restriction of active flexion of the MCP joint of the affected ray and the indications for treatment are caused not only by a cosmetic defect, but also functional impairment. Surgical treatment of brachymetacarpia by distraction osteosynthesis gives predictably good results. Complications during the treatment of brachymetacarpia are rare and mostly related to the appearance of contractures, in order to prevent which in the postoperative period should be used preventive conservative therapy.Цель работы: изучение морфо-функциональных изменений верхних конечностей при брахиметакарпии, оценка косметических и функциональных нарушений и анализ результатов лечения пациентов с данной патологией. Материал и методы. Представлены результаты обследования и хирургического лечения шести пациентов (10 кистей, укорочение 18 пястных костей) с брахиметакарпией методом дистракционного остеосинтеза. Результаты. У всех пациенток отмечалась неудовлетворенность косметическим состоянием кисти и усталость при физических нагрузках на кисть. IV луч был укорочен в 50% случаев, V луч - в 33% и III луч - в 17%. Ограничение активного сгибания отмечалось у всех пациентов, в среднем флексия составила 58,9±7,1°. После лечения сгибание увеличилось в среднем на 20,5° (22,7%). Осложнения были получены у двух пациентов (на трех кистях). Выводы. Брахиметакарпия является редким заболеванием, этиология которого до сих пор является неизвестной и требует дальнейшего изучения. Во всех случаях при брахиметакарпии имеется ограничение функции активного сгибания в пястно-фаланговом суставе пораженного луча, и показания к лечению обусловлены не только косметическим дефектом, но и функциональными нарушениями. Оперативное лечение брахиметакарпии методом дистракционного остеосинтеза дает прогнозируемо хорошие результаты. Осложнения при брахиметакарпии редки и преимущественно связаны с возникновением контрактур, с целью предотвращения которых в послеоперационном периоде должна использоваться профилактическая консервативная терапия

АНЕСТЕЗИЯ ПРИ МИКРОХИРУРГИЧЕСКОЙ АУТОТРАНСПЛАНТАЦИИ ПАЛЬЦЕВ СТОПЫ НА КИСТЬ У ДЕТЕЙ С ВРОЖДЕННОЙ И ПОСТТРАВМАТИЧЕСКОЙ ПАТОЛОГИЕЙ

Intraoperative combination of monolateral spinal anesthesia and prolonged brachial plexus block is evaluated in 65 children with autotransplantation of fingers from foot to hand. Variability of heart rhythm demonstrated autonomous stability in the main group. Dynamical study of skin temperature and dopplerographic evaluation demonstrated local sympatholysis in the blocked extremity. Significant improvement of circulation and quality of analgesia is revealed in case of prolonged perineural use of local anesthetics in the postoperative period. Described combination of intra- and postoperative treatment of such patients makes complex treatment more effective.Проанализирована интраоперационная комбинация монолатеральной спинальной анестезии и продленной блокады плечевого сплетения при аутотрансплантации пальцев стопы на кисть у 65 детей. По результатам обследования вариабельности сердечного ритма подтверждена стабильность вегетативного гомеостаза в основной группе. Показан локальный симпатолизис блокируемой конечности исследованиями динамики термометрии и допплерографии. Выявлено выраженное улучшение кровоснабжения и анальгетического компонента при продленном введении местных анестетиков периневрально в послеоперационном периоде. При использовании предложенного метода интра- и послеоперационного ведения больных значимо сократилось количество некрэктомий