Bound hole states in a ferromagnetic (Ga,Mn)As environment

A numerical technique is developed to solve the Luttinger-Kohn equation for impurity states directly in k-space and is applied to calculate bound hole wave functions in a ferromagnetic (Ga,Mn)As host. The rich properties of the band structure of an arbitrarily strained, ferromagnetic zinc-blende semiconductor yields various features which have direct impact on the detailed shape of a valence band hole bound to an active impurity. The role of strain is discussed on the basis of explicit calculations of bound hole states.Comment: 9 pages, 10 figure

Temperature dependent Neel wall dynamics in GaMnAs/GaAs

Extensive Kerr microscopy studies reveal a strongly temperature dependent domain wall dynamics in Hall-bars made from compressively strained GaMnAs. Depending on the temperature magnetic charging of domain walls is observed and nucleation rates depend on the Hall-geometry with respect to the crystal axes. Above a critical temperature where a biaxial-to-uniaxial anisotropy transition occurs a drastic increase of nucleation events is observed. Below this temperature, the nucleation of domains tends to be rather insensitive to temperature. This first spatially resolved study of domain wall dynamics in patterned GaMnAs at variable temperatures has important implications for potential single domain magneto-logic devices made from ferromagnetic semiconductors.Comment: Figures 2 and 6 not correctly TeXifie

Hysteretic magnetoresistance and thermal bistability in a magnetic two-dimensional hole system

Colossal negative magnetoresistance and the associated field-induced insulator-to-metal transition, the most characteristic features of magnetic semiconductors, are observed in n-type rare earth oxides and chalcogenides, p-type manganites, n-type and p-type diluted magnetic semiconductors (DMS) as well as in quantum wells of n-type DMS. Here, we report on magnetostransport studies of Mn modulation-doped InAs quantum wells, which reveal a magnetic field driven and bias voltage dependent insulator-to-metal transition with abrupt and hysteretic changes of resistance over several orders of magnitude. These phenomena coexist with the quantised Hall effect in high magnetic fields. We show that the exchange coupling between a hole and the parent Mn acceptor produces a magnetic anisotropy barrier that shifts the spin relaxation time of the bound hole to a 100 s range in compressively strained quantum wells. This bistability of the individual Mn acceptors explains the hysteretic behaviour while opening prospects for information storing and processing. At high bias voltage another bistability, caused by the overheating of electrons10, gives rise to abrupt resistance jumps

A questionnaire-based (UM-PDHQ) study of hallucinations in Parkinson's disease

Background: Hallucinations occur in 20-40% of PD patients and have been associated with unfavorable clinical outcomes (i.e., nursing home placement, increased mortality). Hallucinations, like other non-motor features of PD, are not well recognized in routine primary/secondary clinical practice. So far, there has been no instrument for uniform characterization of hallucinations in PD. To this end, we developed the University of Miami Parkinson's disease Hallucinations Questionnaire (UM-PDHQ) that allows comprehensive assessment of hallucinations in clinical or research settings.Methods: The UM-PDHQ is composed of 6 quantitative and 14 qualitative items. For our study PD patients of all ages and in all stages of the disease were recruited over an 18-month period. The UPDRS, MMSE, and Beck Depression and Anxiety Inventories were used for comparisons.Results and Discussion: Seventy consecutive PD patients were included in the analyses. Thirty-one (44.3%) were classified as hallucinators and 39 as non-hallucinators. No significant group differences were observed in terms of demographics, disease characteristics, stage, education, depressive/anxiety scores or cognitive functioning (MMSE) between hallucinators and non-hallucinators. Single mode hallucinations were reported in 20/31 (visual/14, auditory/4, olfactory/2) whereas multiple modalities were reported in 11/31 patients. The most common hallucinatory experience was a whole person followed by small animals, insects and reptiles.Conclusion: Using the UM-PDHQ, we were able to define the key characteristics of hallucinations in PD in our cohort. Future directions include the validation of the quantitative part of the questionnaire than will serve as a rating scale for severity of hallucinations

Semiconductor Spintronics

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure

Radiolabeling of the hydrophobic components of lung surfactant with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine

Studies of the metabolism and distribution of lung surfactant are aided by use of radiolabeled surfactant or surfactant components. These studies have often made use of [3H]- or [14C]phosphatidylcholine. Analysis of the lung content of surfactant containing these beta-emitting labels usually requires tissue digestion, use of scintillation fluids, and significant correction for quenching of photon production. Because use of a gamma-emitting isotope would obviate these requirements, we have investigated the use of 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID), a lipophilic photoactivatable compound, to radiolabel pulmonary surfactant. Our results indicate that, during photoactivation, products of [125I]TID are produced that result in radiolabeling of both the lipid and protein components of extracted porcine surfactant. Separation of radiolabeled surfactant from hydrophobic nonlabelling photolysis products was accomplished by gel chromatography. Exposure of surfactant (34 mumol/ml) to [125I]TID under labeling conditions resulted in incorporation of 45.3 +/- 5.1% of the radiolabel. Incorporation of radiolabel in the various phospholipids of lung surfactant was approximately equivalent. Lipophilic surfactant apoproteins were also radiolabeled. Finally, both in vitro and in vivo testing of radiolabeled surfactant (0.1 microCi/mg) revealed full retention of surface tension lowering ability

Effect of N-nitroso-N-methylurethane on gas exchange, lung compliance, and surfactant function of rabbits

OBJECTIVES: To define the effect of N-nitroso-N-methyl-urethane (NNNMU) on pulmonary gas exchange, compliance and the biochemical and functional properties of the lung surfactant system. DESIGN: Four days after inducing lung injury, gas exchange and pulmonary compliance were studied and a bronchoalveolar lavage was taken. SETTING: Experimental laboratory of a university department of medicine, division of pulmonary and critical care medicine. ANIMALS: Ten rabbits after they had received an injection of NNNMU and five control animals. INTERVENTIONS: Controlled mechanical ventilation and bronchoalveolar lavage. MEASUREMENTS AND RESULTS: Measurements of gas exchange (using the multiple inert gas elimination technique), hemodynamics and pulmonary compliance were performed during ventilatory and hemodynamic steady state. A bronchoalveolar lavage (BAL) was taken after sacrificing the animal. BAL samples were processed for cell count and biochemical and functional surfactant analysis. Animals injected with NNNMU developed mild, but significant reduction in PaO2, while maintaining eucapnia during spontaneous air breathing. V/Q distributions and arterial blood gases were similar in all animals when ventilated mechanically with a fixed tidal volume. Compliance of the lung and phospholipid levels in lavage of NNNMU animals was significantly lower than in control animals (CON). Function of surfactant recovered from animals receiving NNNMU was decreased significantly where compared to CON. Thus, NNNMU resulted in a lowered lavage surfactant phospholipid content, impaired surfactant function, decreased compliance and hypoxemia during spontaneous ventilation. However, gas exchange was similar to that of control animals during mechanical ventilation. CONCLUSION: We conclude that NNNMU-induced gas exchange abnormalities present after 4 days are mild and are reversed by fixed volume mechanical ventilation despite marked alteration in surfactant function and lung compliance. These observations further define properties of a lung injury model that is of value in the study of surfactant replacement