Neste trabalho investigamos pela primeira vez flutuações dependentes de spin em correntes eletrônicas polarizadas através de estruturas magnéticas. Nosso sistema físico consiste de uma heteroestrutura com tunelamento ressonante formada por um poço ou \"ponto\" quântico contendo Mn, confinado entre duas barreiras de potencial. Usamos um modelo semiclássico baseado em equações de taxa para calcular as ocupações dos estados ressonantes up e down. Estas equações são derivadas de uma equação mestra que descreve a probabilidade de ocupação dos estados de spin em um dado tempo. Funções correlação corrente-corrente são expressas em termos das funções correlação hop-hop (associadas à transições entre os níveis ressonantes up e down) e o shot noise dependente de spin é determinado em termos da matriz variância do sistema, também derivada da equação mestra. Quando consideramos um feixe polarizado e tempos distintos (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593), podemos obter ambas \"correlações positivas\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8805 0) e/ou \"negativas\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8804 0) no nosso modelo. A generalização e reinterpretação do modelo de ilhas nos possibilitou (i) investigar flutuações dependentes de spin em correntes polarizadas; (ii) observar aumento e atenuação do shot noise; (iii) verificar que processos de \"spin-flip\" com (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593) são relevantes na atenuação do shot noise e (iv) verificar que o ruído contém informações sobre o processo de \"spin-flip\" / In this work we investigate for the first time spin-dependent fluctuations in spin-polarized electronic currents through magnetic structures. Our physical model consists of a resonant-tunneling heterostructure formed by a Mn-based quantum well or \"point\", confined between a double-barrier potential. We used a semiclassical model based on rate equations to calculate the occupations of the spin-up and spindown resonant states. These equations are derived from a master equation describing the probability of occupation of the spin states at a given time. Current-current correlation functions are expressed in terms of hop-hop correlation functions (for hops between islands representing the up and down states) and the spin-dependent shoi noise is determined in terms of the variance matrix of the system; also derived from the master equation. When we consider a polarized beam and distinctive times (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593), we can obtain both \"positive correlations\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8805 0) and \"negative correlations\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8804 0) in our model. The generalization and reinterpretation of the island model allowed us (i) to investigate spin-dependent fluctuations in spinpolarized electronic currents; (ii) to observe enhancement and suppression of shot noise; (iii) to verify that spin-flip processes with (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593) are relevant to shotnoise suppression and (iv) to verify that noise contains information about spin-flip processes

Understanding and manipulating nanosized particles is crucial for the advancement of nanotechnology research. Dependent light scattering of noble metals can be used to achieve new material responses that can be used in different applications. Dependent light scattering of nanoparticles allows the understanding of orientation and location of closely positioned particles. Besides, dependently scattering metallic particles create significantly enhanced near fields and high absorption rates when excited at their plasmon resonance. It is used for spectrally selective heating and melting of nanosized particles as a nanomanufacturing method. With numerical methods dependent scattering properties of particles can be obtained. In this study, the dependent optical absorption efficiencies of metallic nanoparticles are obtained with the newly developed Integrated Poynting Vector Approach (IPVA). This is used in conjunction with a numerical light scattering solution tool DDSCAT. Results indicate that IPVA and DDSCAT together can be used for the estimation of scattering and absorption of nanoparticles affected by the near field of other particles in their close vicinity. The method is suggested to be suitable for the understanding of physical mechanisms behind dependent scattering prior to experiments that require lots of effort and resources.

This dissertation describes the theoretic studies of magnetic moment and spinorbit interaction in vacuum (Dirac wavepacket) and solid state systems, such as semiconductors. The semiclassical approach developed here provides a simple and intuitive picture for the origin of spin and spin-orbit coupling. In the Dirac model, the spin magnetic moment is originated from the self-rotating Dirac wavepacket with a correct g-value. The spin-orbit interaction is related to Berry connection (gauge potential) and the model is generalized to solid state systems. The Rashba effect caused by the spin-orbit coupling in a crystal with asymmetric potential in heterostructure quantum well is calculated by semiclassical spindependent scattering. The exact treatment of interface phase accumulation provides a justification of spin-dependent boundary condition at interface derived in previous treatment using Löwdin decomposition. Other spin-orbit coupling related phenomena in solid state system are also discussed in this thesis. / text

Neste trabalho investigamos pela primeira vez flutuações dependentes de spin em correntes eletrônicas polarizadas através de estruturas magnéticas. Nosso sistema físico consiste de uma heteroestrutura com tunelamento ressonante formada por um poço ou \"ponto\" quântico contendo Mn, confinado entre duas barreiras de potencial. Usamos um modelo semiclássico baseado em equações de taxa para calcular as ocupações dos estados ressonantes up e down. Estas equações são derivadas de uma equação mestra que descreve a probabilidade de ocupação dos estados de spin em um dado tempo. Funções correlação corrente-corrente são expressas em termos das funções correlação hop-hop (associadas à transições entre os níveis ressonantes up e down) e o shot noise dependente de spin é determinado em termos da matriz variância do sistema, também derivada da equação mestra. Quando consideramos um feixe polarizado e tempos distintos (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593), podemos obter ambas \"correlações positivas\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8805 0) e/ou \"negativas\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8804 0) no nosso modelo. A generalização e reinterpretação do modelo de ilhas nos possibilitou (i) investigar flutuações dependentes de spin em correntes polarizadas; (ii) observar aumento e atenuação do shot noise; (iii) verificar que processos de \"spin-flip\" com (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593) são relevantes na atenuação do shot noise e (iv) verificar que o ruído contém informações sobre o processo de \"spin-flip\" / In this work we investigate for the first time spin-dependent fluctuations in spin-polarized electronic currents through magnetic structures. Our physical model consists of a resonant-tunneling heterostructure formed by a Mn-based quantum well or \"point\", confined between a double-barrier potential. We used a semiclassical model based on rate equations to calculate the occupations of the spin-up and spindown resonant states. These equations are derived from a master equation describing the probability of occupation of the spin states at a given time. Current-current correlation functions are expressed in terms of hop-hop correlation functions (for hops between islands representing the up and down states) and the spin-dependent shoi noise is determined in terms of the variance matrix of the system; also derived from the master equation. When we consider a polarized beam and distinctive times (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593), we can obtain both \"positive correlations\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8805 0) and \"negative correlations\" (&#8249 &#916 &#8593 &#916 &#8595 &#8250 &#8804 0) in our model. The generalization and reinterpretation of the island model allowed us (i) to investigate spin-dependent fluctuations in spinpolarized electronic currents; (ii) to observe enhancement and suppression of shot noise; (iii) to verify that spin-flip processes with (&#964 &#8593 &#8595 &#8800 &#964 &#8595 &#8593) are relevant to shotnoise suppression and (iv) to verify that noise contains information about spin-flip processes

No description available.

Nanometer-scale particles of the noble metals have been used for decades as contrast enhancement agents in electron microscopy. Over the past several years it has been demonstrated that these particles also function as excellent contrast agents for optical imaging techniques. The resonant optical scattering they exhibit enables scattering cross sections that may be many orders of magnitude greater than the analogous efficiency factor for fluorescent dye molecules. Biologically relevant labeling with nanoparticles generally results in aggregates containing a few to several tens of particles. The electrodynamic coupling between particles in these aggregates produces observable shifts in the resonance-scattering spectrum. This dissertation provides a theoretical analysis of the scattering from nanoparticle aggregates. The key objectives are to describe this scattering behavior qualitatively and to provide numerical codes usable for modeling its application to biomedical engineering. Considerations of the lowest-order dipole-dipole coupling lead to simple qualitative predictions of the behavior of the spectral properties of the optical cross sections as they depend on number of particles, inter-particle spacing, and aggregate aspect ratio. More comprehensive analysis using the multiple-particle T-matrix formalism allows the elaboration of more subtle cross-section spectral features depending on the interactions of the electrodynamic collective-modes of the aggregate, of individual-particle modes, and of modes associated with groups of particles within the aggregate sub-structure. In combination these analyses and the supporting numerical code-base provide a unified electrodynamic approach which facilitates interpretation of experimental cross section spectra, guides the design of new biophysical experiments using nanoparticle aggregates, and enables optimal fabrication of nanoparticle structures for biophysical applications. / text

Es werden ab-initio Rechnungen des Supermagnetwiderstands-Effektes von Fe/Cr-Multilagen vorgestellt. Die Elektronenstruktur wurde im Rahmen einer LCAO-Superzellen-Rechnung bestimmt. Als Störung der idealen Schichtstruktur wurden Cr-Defekte in Fe angenommen, die durch spinabhängige Relaxationszeiten beschrieben werden. Die elektrischen Transportkoeffizienten wurden durch Lösung der linearisierten Boltzmann-Gleichung in Relaxationszeitnäherung unter Verwendung des Mott-schen Zweistrommodells berechnet. Bei den betrachteten Systemen variierte die Dicke der Fe-Schicht zwischen 3 und 9 Monolagen, die der Cr-Schicht zwischen 1 und 13 Monolagen. In Abhängigkeit von der Fe- bzw. Cr-Schichtdicke ergeben sich in Übereinstimmung mit den Experimenten charakteristische Oszillationen des Supermagnetwiderstandes. Es wird der Einfluß der Spinanisotropie der Streuung auf den Effekt untersucht. Insbesondere kann gezeigt werden, daß der Effekt auch für spinunabhängige Streuung existiert. / Ab-initio calculations of the Giant Magnetoresistance (GMR) for Fe/Cr multilayers are presented. The electronic structure of the Fe/Cr superlattice is calculated within an optimized LCAO scheme using the local spin density approximation. The scattering of the electrons by Cr impurities in an Fe environment is taken into account by spin dependent relaxation times. The transport is described quasiclassically by solving the linearized Boltzmann equation in relaxation time approximation. In agreement with experiments characteristic oscillations of the GMR are obtained in dependence on the Cr and Fe layer thickness. It can be shown, that the GMR can be reduced or increased by the spin anisotropy of the scattering, but the phenomenon still exists for spin-independent scattering.