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Previous issue date: 2015-06-30 / FACEPE / Recentes progressos na fabrica¸c˜ao de nanoestruturas fornecem a possibilidade de produzir
filmes finos que contenham defeitos artificiais como s´ıtios de aprisionamento com tamanho,
geometria e disposi¸c˜ao espacial bem definidas. O estudo dessa introdu¸c˜ao de um arranjo regulardedefeitosemfilmesfinossupercondutoresdotipoIItemsidoativamentedesenvolvido
desde o ponto de vista te´orico e experimental, por um lado pela riqueza de comportamentos
est´aticos e dinˆamicos que apresenta e, por outro, pela compreens˜ao dos mecanismos para
estabilizareancorararededev´orticescontraasfor¸casmotorasexternas. Umdosfenˆomenos
mais not´aveis destes sistemas ´e chamado efeito matching, o qual ocorre quando o n´umero
de v´ortices ´e um m´ultiplo inteiro do n´umero dos centros de aprisionamento, sendo observados
picos na corrente cr´ıtica (resposta est´atica) ou atenua¸c˜oes na mobilidade dos v´ortices
(resposta dinˆamica) nos valores de campo onde esta condi¸c˜ao ´e satisfeita. Nesses campos
comensur´aveis, os v´ortices podem formar uma rede altamente ordenada onde as intera¸c˜oes
v´ortice-v´ortice que reduzem o ancoramento efetivo s˜ao minimizadas. Usando simula¸c˜oes
dedinˆamicamolecular,analisamosasconfigura¸c˜oesdosv´orticeseosefeitosdepinning artificialnadinˆamicadev´orticesemumfilmefinosupercondutordotipoII,comumadistribui¸c˜ao
peri´odica de centros de pinning. A dinˆamica de v´ortices e suas configura¸c˜oes estruturais,
foram simuladas usando o algoritmo de dinˆamica de Langevin. As intera¸c˜oes entre v´ortices
foram modeladas dentro da aproxima¸c˜ao de London com condi¸c˜oes de contorno peri´odicas.
Na parte inicial do estudo, calculamos as configura¸c˜oes de equil´ıbrio para a rede de v´ortices,
encontrando resultados similares aos estudados em trabalhos anteriores. Inclusive, observamos
em nossas simula¸c˜oes que o n´umero de satura¸c˜ao dos centros de ancoragem, i.e. o
n´umero m´aximo de v´ortices aprisionados por cada centro, ´e fun¸c˜ao do campo externo.
de aprisionamento. Esse estudo revela que os tipos de comensurabilidades encontradas
nesse problema dinˆamico s˜ao, em geral, diferentes daqueles encontrados no problema
est´atico. Portanto, a pr´atica usual na literatura de se inferir sobre as configura¸c˜oes est´aticas
dos v´ortices a partir de medidas de magnetorresistˆencia deve ser revista. / Recent progress in manufacturing of nanostructures provides the possibility to produce thin films
containing artificial defects as pinning sites with well-defined size, geometry and spatial arrangement.
The study of the introduction of a regular arrangement of defects in type II superconducting
thinfilmshasbeenactivelydevelopedfromatheoreticalandexperimentalpointofview,ononeside
due to the richness of static and dynamic behaviors that it presents and, second, by understanding
themechanismstostabilizeandanchorthenetworkofvorticesagainstexternaldrivingforces. One
ofthemostremarkablephenomenaofthesesystemsiscalledmatching effectwhichoccurswhenthe
number of vortices is a multiple integer of the number of pinning centers, with peaks observed in
the cr´ıtical current (static response) or the attenuation of the vortices mobility (dynamic response)
values in field where this condition is satisfied. These measurable fields, the vortices can form a
highly ordered network where the vortex-vortex interactions that reduce the effective anchoring
are minimized. Using molecular dynamics simulations, we analyzed the settings of the vortices
and the effects of artificial pinning at the dynamics of vortices in a type II superconducting thin
film with a periodic distribution of pinning centers. The dynamics of vortices and their structural
configurations were simulated using the Langevin dynamics algorithm.
hm. The interactions between
vortices were modeled using London’s approach with periodic boundary conditions. In the early
part of the study, we calculated the balance settings for the vortex network, finding results similar
to those studied in previous works. In fact, we observed in our simulations that the number of
saturation of the anchoring centers, i.e. the maximum number of vortices trapped by each center,
is a function of the external field. This result had already been predicted in calculations performed
within the Ginzburg-Landau formalism. Here, we show that the same effect can be reproduced
at the London scheme. In the second part of the study, we analyzed the dynamics when an
external force is applied in the longitudinal direction relative to the symmetry of the network of
traps. We show that this system displays dynamic commensurability effects when the settings of
the vortices coincide with the periodicity of the arrangement, through the magnetoresistance curves
that have a number of features in the different fields of matching. Certain field values, it falls
in tension are absent due to the particular configuration of vortices and the interaction between
interstitial vortices with the vortices occupying the pinning centers.
This study shows that
the types of measurability found in this dynamic problem are generally different from those found
in the static problem. Therefore, the usual practice in the literature to infer the static settings of
vortices from magnetoresistance measures should be reviewed.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufpe.br:123456789/18324 |
| Date | 30 June 2015 |
| Creators | MATEUS, Fania Danitza Caicedo |
| Contributors | http://lattes.cnpq.br/8076432608646837, SILVA, Clécio Clemente de Souza |
| Publisher | Universidade Federal de Pernambuco, Programa de Pos Graduacao em Fisica, UFPE, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Breton |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFPE, instname:Universidade Federal de Pernambuco, instacron:UFPE |
| Rights | Attribution-NonCommercial-NoDerivs 3.0 Brazil, http://creativecommons.org/licenses/by-nc-nd/3.0/br/, info:eu-repo/semantics/openAccess |
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