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Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. On t.p. "x̲" is subscript. Document formatted into pages; contains ix, 93 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 89-92).

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Orientador: Ezequiel Costa Siqueira / Banca: Victor Ciro Solano Reynoso / Banca: Rodrigo Yoshikawa Oeiras / Resumo: Neste trabalho é proposto a investigação teórica de uma junção formada por metal supercondutor e um metal ferromagnético acoplados através de dois canais. O primeiro canal consiste de um acoplamento direto entre os metais, enquanto que o segundo canal é formado através um ponto quântico composto por um nível discreto. Para isso utilizamos como ferramenta as funções de Green de não-equilíbrio, por meio das quais obtemos o cálculo e as curvas para a corrente elétrica, números de ocupação e transmitância. É demonstrado que podemos alterar o tipo de spin no ponto quântico, e este sobrevive a presença de um campo magnético por meio de um efeito de interferência. Por meio deste resultado, é possível manipular um spin em um ponto quântico por meio de variáveis externas, o que pode ser de interesse em aplicações na computação quântica / Abstract: In this work is proposed the theorical investigation of a double-path junction formed by a ferromagnetic and a supercondutor lead. The first path connects superconductor and ferromagnet by an insulator barrier while in the second path these metals are connected by a single level quantum dot. We have used the nonequilibrium Green's functions to perform the calculations as well as to obtain the curves for electrical current, occupation numbers and transmittance. It is shown that the spin within the quantum dot can be manipulated by means of external parameters which can be of interesed in quantum computation applications / Mestre

Inelastic neutron scattering measurements by Okazaki, Tuberfield, and Stevenson (1964) of the antiferromagnetic spin wave energy, spectrum in manganese fluoride crystal at low temperatures, agree with the results predicted by a dispersion relation introduced without proof in their paper. In this thesis the question is considered in detail to what extent this dispersion relation is justified. The interaction between the manganese ions is described by the Heisenberg exchange Hamiltonian. Following Holstein and Primakoff's formalism the spin deviation operators are introduced and the part of the Hamiltonian ℋ[superscript B] containing all the terms up to those bilinear in the spin deviation operators is diagonalised by means of the Anderson transformation. A correction is next obtained by retaining the diagonal part of those terms which are quadrilinear in the spin deviation operators. Under certain conditions it is shown that ℋ[superscript B] together with the correction term give rise to, a dispersion relation which is identical with that used by Okazaki et al. (1964). Finally the validity of the approximations is also discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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