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Spin Polarization (spin + polarization)
Kinds of Spin Polarization Selected AbstractsRobustness of Spin Polarization in Graphene-Based Spin ValvesADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Masashi Shiraishi Abstract The decrease of spin polarization in spintronics devices under the application of a bias voltage is one of a number of currently important problems that should be solved. Here, an unprecedented robustness of the spin polarization in multilayer-graphene spin valves at room temperature is revealed. Surprisingly, the spin polarization of injected spins is constant up to a bias voltage of +2.7,V and ,0.6,V in positive- and negative-bias voltage applications at room temperature, respectively, which is superior to all spintronics devices. This finding is induced by suppression of spin scattering due to an ideal-interface formation. Furthermore, an important accordance between theory and experiment in molecular spintronics is found by observing the fact that the signal intensity in a local scheme is double that in a nonlocal scheme, as theory predicts, which provides construction of a steadfast physical basis in this field. [source] Spin polarization of a non-magnetic high g-factor semiconductor at low magnetic fieldPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007J. Lee Abstract We have studied the spin polarization of HgCdTe by measuring Shubnikov-de Haas oscillations. The magnetic field have been applied in parallel and perpendicular to the current. Relatively long spin relaxation time was observed since only spin conserved transition is allowed by selection rules. The electronic spin is completely polarized when the applied magnetic field is larger than 0.5 Tesla, which can be easily generated by micromagnets deposited on the surface of the specimen. Thus, the spin-manipulation such as spin up/down junction can be realized with this semiconductor. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin polarization and electronic structure of ferromagnetic Mn5Ge3 epilayersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2005R. P. Panguluri Abstract Germanium-based alloys hold great promise for future spintronics applications, due to their potential for integration with conventional Si-based electronics. High-quality single phase Mn5Ge3(0001) films, grown by solid-phase epitaxy on Ge(111) and GaAs(111), exhibit strong ferromagnetism up to the Curie temperature TC , 296 K. Point Contact Andreev Reflection (PCAR) measurements on Mn5Ge3 epilayers reveal a spin-polarization P = 42 ± 5% for both substrates. We also calculate the spin polarization of bulk Mn5Ge3 in the diffusive and ballistic regimes using density-functional theory (DFT). The measured spin polarization exceeds the theoretical estimates of PDFT = 35 ± 5% and 10 ± 5% for the diffusive and ballistic limits, respectively. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin polarization in a single InAs/InP quantum dotPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006Weidong Sheng Abstract We report on a theoretical study of the spin properties of electrons and holes in a single InAs/InP selfassembled quantum dot by means of an empirical tight-binding method. When the magnetic field is varied from the Faraday to Voigt configuration, electrons and holes are found to exhibit different spin polarization: the electron spin is found to follow the direction of the magnetic field while the hole spin is frozen along the growth direction of the dot. The frozen spin of holes is attributed to the dominant heavy-hole component in the hole states, which also leads to a zero in-plane g factor of holes. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Robustness of Spin Polarization in Graphene-Based Spin ValvesADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Masashi Shiraishi Abstract The decrease of spin polarization in spintronics devices under the application of a bias voltage is one of a number of currently important problems that should be solved. Here, an unprecedented robustness of the spin polarization in multilayer-graphene spin valves at room temperature is revealed. Surprisingly, the spin polarization of injected spins is constant up to a bias voltage of +2.7,V and ,0.6,V in positive- and negative-bias voltage applications at room temperature, respectively, which is superior to all spintronics devices. This finding is induced by suppression of spin scattering due to an ideal-interface formation. Furthermore, an important accordance between theory and experiment in molecular spintronics is found by observing the fact that the signal intensity in a local scheme is double that in a nonlocal scheme, as theory predicts, which provides construction of a steadfast physical basis in this field. [source] Dilute Doping, Defects, and Ferromagnetism in Metal Oxide SystemsADVANCED MATERIALS, Issue 29 2010Satishchandra B. Ogale Over the past decade intensive research efforts have been carried out by researchers around the globe on exploring the effects of dilute doping of magnetic impurities on the physical properties of functional non-magnetic metal oxides such as TiO2 and ZnO. This effort is aimed at inducing spin functionality (magnetism, spin polarization) and thereby novel magneto-transport and magneto-optic effects in such oxides. After an early excitement and in spite of some very promising results reported in the literature, this field of diluted magnetic semiconducting oxides (DMSO) has continued to be dogged by concerns regarding uniformity of dopant incorporation, the possibilities of secondary ferromagnetic phases, and contamination issues. The rather sensitive dependence of magnetism of the DMSO systems on growth methods and conditions has led to interesting questions regarding the specific role played by defects in the attendant phenomena. Indeed, it has also led to the rapid re-emergence of the field of defect ferromagnetism. Many theoretical studies have contributed to the analysis of diverse experimental observations in this field and in some cases to the predictions of new systems and scenarios. In this review an attempt is made to capture the scope and spirit of this effort highlighting the successes, concerns, and questions. [source] On the electronic structure and bonding of the intriguing mixed Fe2+/Fe3+ [{Cp(CO)2Fe}tBuPO2FeCl2]2 -Complex,HETEROATOM CHEMISTRY, Issue 5 2005Ingo-Peter Lorenz The structure and bonding of [{Cp(CO)2Fe}tBuPO2FeCl2]2(2) have been investigated theoretically and experimentally. The molecular orbitals of 2 have been calculated to investigate the question why this type of complex forms a planar ring system. The electronic configuration of different electronic states, spin polarization, and bonding of 2 are discussed. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:398,405, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20109 [source] The magnetic moments and their long-range ordering for Fe atoms in a wide variety of metallic environmentsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010A. Ayuela Abstract The magnitudes of Fe magnetic moments, together with their long-range ordering when appropriate, are compared and contrasted in a variety of metallic environments. Thus, Fe, in its stable body-centered-cubic (bcc) phase under ambient conditions, is considered under pressures p, which can yield different crystal structures at high p, including fcc. The modification of the ferromagnetism in bcc Fe is surveyed as one passes through a bc-tetragonal lattice to the fcc form. In the latter, evidence is presented, both from theory and experiment, that the ordering is antiferromagnetic in character. Then, binary metallic alloys with Fe atoms as the majority component are considered, Fe,Co and Fe,Ga being focal points in both ordered and disordered materials. Finally, some discussion is given, involving again both experiment and theory, of the possible spin polarization of neighboring Cs atoms when Fe impurity atoms are inserted into the low conduction electron density characterizing this heavy alkali metal under ambient conditions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Spin states in polynuclear clusters: The [Fe2O2] core of the methane monooxygenase active siteJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2006Carmen Herrmann Abstract The ability to provide a correct description of different spin states of mono- and polynuclear transition metal complexes is essential for a detailed investigation of reactions that are catalyzed by such complexes. We study the energetics of different total and local spin states of a dinuclear oxygen-bridged iron(IV) model for the intermediate Q of the hydroxylase component of methane monooxygenase by means of spin-unrestricted Kohn,Sham density functional theory. Because it is known that the spin state total energies depend systematically on the density functional, and that this dependence is intimately connected to the exact exchange admixture of present-day hybdrid functionals, we compare total energies, local and total spin values, and Heisenberg coupling constants calculated with the established functionals BP86 and B3LYP as well as with a modified B3LYP version with an exact exchange admixture ranging from 0 to 24%. It is found that exact exchange enhances local spin polarization. As the exact exchange admixture increases, the high-spin state is energetically favored, although the Broken-Symmetry state always is the ground state. Instead of the strict linear variation of the energy splittings observed for mononuclear complexes, a slightly nonlinear dependence is found. The Heisenberg coupling constants JFe1Fe2,evaluated according to three different proposals from the literature,are found to vary from ,129 to ,494cm,1 accordingly. The experimental finding that intermediate Q has an antiferromagnetic ground state is thus confirmed. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1223,1239, 2006 [source] A method for controlling the spins of atoms using optical near-fieldsJOURNAL OF MICROSCOPY, Issue 3 2003A. Shojiguchi Summary On the basis of the procedure for controlling the spins of atoms using circularly polarized evanescent light proposed by Hori et al.[(1996) Abstracts of the 1st Asia-Pacific Workshop on Near-field Optics] we discuss the influence of boundary conditions on the probability of spontaneous emission and thus on the spin polarization efficiency, which was not considered in the Hori et al. study. Using the Carniglia,Mandel mode expansion of electromagnetic fields, we derive the spontaneous emission and spin polarization probabilities of atoms near a dielectric surface, and show the atom,surface distance dependence and refractive index dependence. Numerical evaluation for the 6P1/2,6S1/2 transition of a Cs atom indicates an increase in the efficiency of spin polarization by 30%. [source] Parahydrogen-induced polarization in imaging: Subsecond 13C angiographyMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001K. Golman Abstract High nuclear spin polarization of 13C was reached in organic molecules. Enhancements of up to 104, compared to thermal polarization at 1.5 T, were achieved using the parahydrogen-induced polarization technique in combination with a field cycling method. While parahydrogen has no net polarization, it has a high spin order, which is retained when hydrogen is incorporated into another molecule by a chemical reaction. By subjecting this molecule to a sudden change of the external magnetic field, the spin order is transferred into net polarization. A 13C angiogram of an animal was generated in less than a second. Magn Reson Med 46:1,5, 2001. © 2001 Wiley-Liss, Inc. [source] Spin-filtering effect in a two-dimensional electron gas under a local fringe fieldPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Seon-Gu Huh Abstract We fabricated a spin-filtering device which consists of InAs based two-dimensional electron gas and two ferromagnetic pads. A fringe field at the edge of a ferromagnetic pad was used to induce spin polarization of the moving electrons in a two-dimensional electron gas. The direction of the fringe field was determined by the magnetization of the ferromagnetic pad, which was switched by using the external magnetic field. A current of which spins were aligned by one fringe field (polarizer) was filtered by the other fringe field (analyzer). The resistance of the device was in either a high state or a low state depending on the alignment of the fringe fields. The spin-filtering effect diminishes rapidly as the thermal energy exceeds the Zeeman splitting. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photon-assisted tunneling in ac driven double quantum dot spin pumpsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006R. Sánchez Abstract In this work, we study the effect of an applied ac gate voltage on the spin filtering and pumping properties of a lateral double quantum dot, in the Coulomb blockade and weak coupling regimes, considering not only the effect of the ac potential on the inter-dot tunneling but also on the tunneling through the leads. This last effect accounts for additional photon absorption and emission processes and therefore affects the spin polarization of the pumped current. In particular, we find that the spin down filtering property can be affected depending on the intensity of the ac field. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin polarization of a non-magnetic high g-factor semiconductor at low magnetic fieldPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007J. Lee Abstract We have studied the spin polarization of HgCdTe by measuring Shubnikov-de Haas oscillations. The magnetic field have been applied in parallel and perpendicular to the current. Relatively long spin relaxation time was observed since only spin conserved transition is allowed by selection rules. The electronic spin is completely polarized when the applied magnetic field is larger than 0.5 Tesla, which can be easily generated by micromagnets deposited on the surface of the specimen. Thus, the spin-manipulation such as spin up/down junction can be realized with this semiconductor. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic ordering of Mn and Ru in (La0.52Ba0.48) (Mn0.51Ru0.49)O3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007S. Y. Wu The cover picture of the current issue relates to the article by S. Y. Wu et al. [1]. The authors study the crystal structure and magnetic properties of a polycrystalline (La0.52Ba0.48) (Mn0.51Ru0.49)O3 sample. The critical temperatures of Ru and Mn were determined using the temperature dependent peak intensities. Neutron magnetic diffraction measurements show anomalies that are associated with the ferromagnetic ordering of the Mn and Mn/Ru spins, respectively, with the spin magnetic moments (shown as arrows) either parallel or at an inclined angle to the c -axis direction. The corresponding author Sheng Yun Wu is Assistant Professor at the Department of Physics of the National Dong Hwa University in Hualien, Taiwan. His research interests include the study of magnetic properties in perovskite system and spin polarization of closed d-shell nanoparticles. [source] Spin polarization and electronic structure of ferromagnetic Mn5Ge3 epilayersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2005R. P. Panguluri Abstract Germanium-based alloys hold great promise for future spintronics applications, due to their potential for integration with conventional Si-based electronics. High-quality single phase Mn5Ge3(0001) films, grown by solid-phase epitaxy on Ge(111) and GaAs(111), exhibit strong ferromagnetism up to the Curie temperature TC , 296 K. Point Contact Andreev Reflection (PCAR) measurements on Mn5Ge3 epilayers reveal a spin-polarization P = 42 ± 5% for both substrates. We also calculate the spin polarization of bulk Mn5Ge3 in the diffusive and ballistic regimes using density-functional theory (DFT). The measured spin polarization exceeds the theoretical estimates of PDFT = 35 ± 5% and 10 ± 5% for the diffusive and ballistic limits, respectively. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of spin state in a quantum dot by using strongly asymmetric tunnel barriersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003T. Hayashi Abstract We investigate the spin state of a GaAs lateral quantum dot (QD) by using strongly asymmetric tunnel barriers. The saturated current depends on the current polarity, which switches the direction of the dominant tunneling transition that increases or decreases the total spin. With this technique, the spin polarization and the Coulomb interaction are investigated. We find that high spin states appearing in some magnetic field regions can be understood by considering simple Coulomb interactions. [source] Polarized electrons, trions, and nuclei in charged quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003A. S. Bracker Abstract We have investigated spin polarization in GaAs quantum dots. Excitons and trions are polarized directly by optical excitation and studied through polarization of photoluminescence. Electrons and nuclei are polarized indirectly through subsequent relaxation processes. Polarized electrons are identified by the Hanle effect for exciton and trion photoluminescence, while polarized nuclei are identified through the Overhauser effect in individual charged quantum dots. [source] Nuclear field effect on the spin dynamics of electron localized on a donor in a single quantum wellPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2008C. Testelin Abstract We use photoinduced Faraday rotation (PFR) in presence of an applied magnetic field to study the spin dynamics of localized electrons. The sample is a CdTe/CdMgTe quantum well (QW) of width 80 Ĺ containing a layer of iodine donors at its center, with concentration 1011 cm,2. The spin polarization of donor-bound electrons is built via the optical polarization of donor-bound excitons, their hole spin relaxation, and their recombination. In a transverse (in-plane) magnetic field, PFR shows damped Larmor oscillations from which we deduce a 18 ns electron-spin decoherence time, and a transverse Landé factor of 1.29. In addition, for oblique optical incidence the electron-nuclei hyperfine interaction builds a nuclear spin polarization in presence of polarized electrons. This leads to the construction of an effective magnetic field, the Overhauser field, acting on the electronic spins. The Larmor frequency is then different for ,+ or ,, polarizations of the exciting light. The dependence of the phenomenon on the optical incidence allows the determination of the maximal Overhauser field, which is about 10 mT, at least two orders of magnitude weaker than for III-V semiconductors. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Strong spin relaxation length dependence on electric field gradientsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006D. Csontos Abstract We discuss the influence of electrical effects on spin transport, and in particular the propagation and relaxation of spin polarized electrons in the presence of inhomogeneous electric fields. We show that the spin relaxation length strongly depends on electric field gradients, and that significant suppression of electron spin polarization can occur as a result thereof. A discussion in terms of a drift-diffusion picture, and selfconsistent numerical calculations based on a Boltzmann-Poisson approach shows that the spin relaxation length in fact can be of the order of the charge screening length. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Overhauser shift in photoluminescence of excitons with fine structure from a single self-assembled InAlAs quantum dotPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006T. Mukumoto Abstract We report optical pumpingof nuclear spinpolarizationinasingle self-assembledIn0.75Al0.25As/Al0.3Ga0.7As quantum dot where the exciton has a fine structure. Through the change of state mixing that is induced by the anisotropic exchange interaction and the applied magnetic field, the relationship between the magnitude of the Overhauser shift and the optically injected electron spin polarization is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin polarization in a single InAs/InP quantum dotPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006Weidong Sheng Abstract We report on a theoretical study of the spin properties of electrons and holes in a single InAs/InP selfassembled quantum dot by means of an empirical tight-binding method. When the magnetic field is varied from the Faraday to Voigt configuration, electrons and holes are found to exhibit different spin polarization: the electron spin is found to follow the direction of the magnetic field while the hole spin is frozen along the growth direction of the dot. The frozen spin of holes is attributed to the dominant heavy-hole component in the hole states, which also leads to a zero in-plane g factor of holes. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Co2MnSi as full Heusler alloy ferromagnetic electrode in magnetic tunneling junctionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2006G. Reiss Abstract The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunneling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunneling resistance, where a strong dependence of the tunneling current on an external magnetic field can be found. In order to obtain large magnetoresistance effects, materials with strongly spin polarized electron gas around the Fermi level have to be found. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co2MnSi. First, experimental aspects of the integration of this alloy in magnetic tunneling junctions will be addressed. With these junctions, we obtain up to 100% TMR at low temperature. The current status of this research will then be summarized with special regard to the complex diffusion mechanisms occurring in these devices and to the properties of the interfaces between the Heusler material and the insulator. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Polarization of electron spin in two barrier system based on semimagnetic semiconductorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006S. B. Lev Abstract The spin-dependent tunneling of electrons through a two barrier semiconductor heterostructure with a semimagnetic layer was investigated. It was shown that the resonant level splitting in the semimagnetic well under an external magnetic field allows achieving a high level of spin polarization of the current flowing through the proposed spin filter. The dependence of the polarization depth on the parameters of the sample was calculated in the two component diffusion transport model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin-polarized resonant tunneling through two coupled quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2006P. Trocha Abstract Resonant electronic transport through two coupled non-interacting single-level quantum dots attached to ferromagnetic leads with collinear magnetizations is analyzed theoretically. Coupling of the dots to external leads as well as the inter-dot coupling are assumed to be spin dependent. Basic transport characteristics, including current-voltage curves, linear and nonlinear conductance, and tunnel magnetoresistance associated with magnetization rotation are calculated using the Green function technique. The relevant Green functions have been calculated by the equation of motion method. Variation of the transport characteristics with such system parameters like energy level position, spin polarization of the leads, and coupling between the dots has been calculated numerically. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The electron-spin,nuclear-spin interaction studied by polarized neutron scatteringACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2007Heinrich B. Stuhrmann Dynamic nuclear spin polarization (DNP) is mediated by the dipolar interaction of paramagnetic centres with nuclear spins. This process is most likely to occur near paramagnetic centres at an angle close to 45° with respect to the direction of the external magnetic field. The resulting distribution of polarized nuclear spins leads to an anisotropy of the polarized neutron scattering pattern, even with randomly oriented radical molecules. The corresponding cross section of polarized coherent neutron scattering in terms of a multipole expansion is derived for radical molecules in solution. An application using data of time-resolved polarized neutron scattering from an organic chromium(V) molecule is tested. [source] Electron-density studies of molecular magnetic materialsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2004Sébastien Pillet For more than forty years, the experimental determination and analysis of electron densities have played a fundamental role in advances in the chemical bond concept. The present paper illustrates the application of this approach to the field of molecular magnetism with examples that recently appeared in the literature. Particular attention is attached to several classes of materials, purely organic free radicals, coordination compounds and organometallic complexes, which exhibit specific magnetic behaviors. It is shown to what extent the electron-density analysis can shed light on bonding aspects that are closely related to magnetic couplings. Relations between spin delocalization, spin polarization, superexchange and the characteristics of the electron density are described. The use of the topological theory of `atoms in molecules' allows the possible magnetic interaction pathways to be located and defined, especially through weak intermolecular contacts. The complementarity with polarized neutron diffraction and spin-density modeling techniques is particularly evident from the chosen examples. [source] Elucidation of structure,function relationships in the lung: contributions from hyperpolarized 3helium MRICLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 6 2002Hans-Ulrich Kauczor Summary Magnetic resonance imaging (MRI) using hyperpolarized 3helium (He) gas as the source of signal provides new physiological insights into the structure,function relationships of the lung. Traditionally, lung morphology has been visualized by chest radiography and computed tomography, whereas lung function was assessed by using nuclear medicine. As all these techniques rely on ionizing radiation, MRI has some inherent advantages. 3He MRI is based on ,optical pumping' of the 3He gas which increases the nuclear spin polarization by four to five orders of magnitude translating into a massive gain in signal. Hyperpolarized 3He gas is administered as an inhaled ,contrast agent' and allows for selective visualization of airways and airspaces. Straightforward gas density images demonstrate the homogeneity of ventilation with high spatial resolution. In patients with lung diseases 3He MRI has shown a high sensitivity to depict ventilation defects. As 3He has some more exciting properties, a comprehensive four-step functional imaging protocol has been established. The dynamic distribution of ventilation during continuous breathing can be visualized after inhalation of a single breath of 3He gas using magnetic resonance (MR) sequences with high temporal resolution. Diffusion weighted 3He MRI provides a new measure for pulmonary microstructure because the degree of restriction of the Brownian motion of the 3He atoms reflects lung structure. Since the decay of 3He hyperpolarization is dependent on the ambient oxygen concentration, regional and temporal analysis of intrapulmonary pO2 becomes feasible. Thus, pulmonary perfusion, ventilation,/perfusion ratio and oxygen uptake can be indirectly assessed. Further research will determine the significance of the functional information with regard to physiology and patient management. [source] Spin dynamics of exciton polaritons in microcavitiesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2005I. A. Shelykh Abstract In this chapter we address a complex set of optical phenomena linked to the spin dynamics of exciton polaritons in semiconductor microcavities. When optically created, polaritons inherit the spin and dipole moment from the exciting light. Their state can be fully characterized by a so-called "pseudospin" accounting for both spin and dipole moment orientation. However, from the very beginning of their life in a microcavity, polaritons start changing their pseudospin state under effect of effective magnetic fields of different nature and due to scattering with acoustic phonons, defects, and other polaritons. This makes pseudospin dynamics of exciton polaritons rich and complex. It manifests itself in non-trivial changes in polarization of light emitted by the cavity versus time, pumping energy, pumping intensity and polarization. During the first years of theoretical research on exciton-polariton relaxation the polarization has been simply neglected. Later it has been understood that the energy and momentum-relaxation of exciton polaritons are spin-dependent. It is typically the case in the regime of stimulated scattering when the spin polarizations of initial and final polariton state have a huge effect on the scattering rate between these states. It appeared that critical conditions for polariton Bose-condensation are also polarization-dependent. In particular, the stimulation threshold (i.e. the pumping power needed to have a population exceeding 1 at the ground state of the lower polariton branch) has been experimentally shown to be lower under linear than under circular pumping. These experimental observations have stimulated the theoretical research toward understanding of mutually dependent polarization- and energy-relaxation mechanisms in microcavities. The authors of this chapter have been working on theoretical description of different specific effects of polariton spin-dynamics in microcavities for years. Here we attempted to put together all fragments and to formulate a general approach to the problem that would allow then to consider a variety of particular cases. We start from reminding the main spin-relaxation mechanisms known for free carriers and excitons. We then overview the most essential experimental results in this field before to present our original formalism which allowed us to interpret the key experimental findings. We are going to discuss only the strong coupling regime leaving aside all polarization effects in VCSELs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Symmetries and anisotropies of the electronic states within full spin,orbit couplingPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005G. E. Marques Abstract We have analyzed how the symmetries and the anisotropies of energy dispersions and of the spinor states, within full spin,orbit interaction, form the two independent circular spin polarizations. We also compare how the effects produced by Rashba and Dresselhauss interaction terms act on the structure of the Hilbert space. These aspects are used to envisage a voltage controlled multichannel spin-filtering regime in nonmagnetic diode structures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||