Publication: Dos casos paradigmáticos de excitaciones colectivas en la banda de conducción: monocristales superconductores y nanoestructuras plasmónicas
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2018-05-21
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Universidad Complutense de Madrid
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Abstract
En esta tesis se han estudiado dos tipos de sistemas cuyas propiedades proceden del comportamiento colectivo de los electrones en la banda de conducción, como son los superconductores y los sistemas plasmónicos. Ambos son ejemplos paradigmáticos de fenómenos colectivos en la banda de conducción y resultan de un gran interés tanto en el terreno de la investigación fundamental como de cara a aplicaciones tecnológicas. Mientras que en el caso de los superconductores hay una interacción mutua entre electrones, ésta no existe para los plasmones. Así, aunque ambos efectos se originan en la banda de conducción, las propiedades características de cada uno de estos sistemas son muy diferentes. Los superconductores estudiados han sido monocristales dopados con níquel del compuesto BaFe2As2. Estos cristales forman parte de la clase de superconductores descubierta más recientemente, los nicturos de hierro. En este tipo de materiales la superconductividad se consigue a partir del dopado del compuesto padre (p. ej. el BaFe2As2 en nuestro caso), de forma análoga a otros sistemas superconductores bien conocidos como son los cupratos. Sin embargo, al contrario que en estos últimos compuestos, la presencia de átomos ferromagnéticos (como el propio hierro, o elementos dopantes como el níquel y el cobalto) en la estructura cristalina no suprime la superconductividad...
In this thesis, two different kinds of systems whose properties arise from a colective behavior of conduction band electrons have been studied. These systems are superconductors and plasmonic materials, both being paradigmatic examples of colective phenomena in the conduction band. These systems are of great interest in the fields of basic research and techonological applications. While for superconductors there is a mutual interaction between electrons, that is not the case for plasmons. Therefore, even when both effects emerge from the conduction band, the characteristic features of each system are quite different. The superconductors studied in this thesis are nickel-doped single crystals of the BaFe2As2 compound. These crystals belong to the most recently discovered group of superconductors: the iron pnictides. In these materials, superconductivity is achieved through doping of the parent compound (i. e. BaFe2As2 in our case), in a similar way than in other wellknown superconducting systems as cuprates. However, the presence of ferromagnetic atoms (such as iron in the parent structure or dopants like nickel and cobalt) in the iron pnictides does not suppress superconductivity, as it happens in cuprates...
In this thesis, two different kinds of systems whose properties arise from a colective behavior of conduction band electrons have been studied. These systems are superconductors and plasmonic materials, both being paradigmatic examples of colective phenomena in the conduction band. These systems are of great interest in the fields of basic research and techonological applications. While for superconductors there is a mutual interaction between electrons, that is not the case for plasmons. Therefore, even when both effects emerge from the conduction band, the characteristic features of each system are quite different. The superconductors studied in this thesis are nickel-doped single crystals of the BaFe2As2 compound. These crystals belong to the most recently discovered group of superconductors: the iron pnictides. In these materials, superconductivity is achieved through doping of the parent compound (i. e. BaFe2As2 in our case), in a similar way than in other wellknown superconducting systems as cuprates. However, the presence of ferromagnetic atoms (such as iron in the parent structure or dopants like nickel and cobalt) in the iron pnictides does not suppress superconductivity, as it happens in cuprates...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 15-06-2017