Supercondutividade na presença de correlações que podem gerar pseudogap
Autor(a) principal: | |
---|---|
Data de Publicação: | 2019 |
Tipo de documento: | Tese |
Idioma: | por |
Título da fonte: | Manancial - Repositório Digital da UFSM |
Texto Completo: | http://repositorio.ufsm.br/handle/1/31398 |
Resumo: | Since the discovery of superconductivity at high temperatures in 1986, the problem of correlations in superconductivity has received a lot of attention, but it remains as an open problem in condensed matter physics. In this work, superconductivity with di erent symmetries is considered in an one-band Hubbard model. Besides the local repulsive interaction, the studied model also presents an attractive potential, which is responsible for the superconductivity. This study was conducted for superconductors with s, dx2�����y2 , and s-extended symmetry. The main objective is to investigate the role of correlations in the normal and superconducting properties of the model. To treat the model, we used the Green's functions technique together with a n-pole approximation. The n-pole approximation was considered in two versions, the original version (R-O) proposed by Roth (Phys. Rev 184 (1969)) and a modi ed version (R-M) (IJMPB 25 (2011)), which describes most appropriate antiferromagnetic correlations associated with the model. In the R-M version, antiferromagnetic correlations may give rise to a pseudogap in the density of states of the normal state. The pseudogap has been a central point in the study of cuprate superconductors because it is believed to be directly associated with the mechanisms responsible for superconductivity in these systems. More speci cally, we investigated how the correlations responsible for the pseudogap scenario a ect the superconducting critical temperature for the di erent symmetries. The obtained results show that superconductors with di erent symmetries are a ected di erently by the correlations. In general, the critical transition temperature Tc is higher in the R-M approximation compared to that of the R-O approximation. Compared to mean eld results, the Tc 's obtained in the n-pole approximations are higher than the mean eld ones. For s symmetry, in the RM approximation, the increasing of the interaction U, suppresses the superconductivity in the region of occupations close to NT = 1; 0 (with NT < 1; 0) and favors superconductivity in an intermediate region of occupation. In this case, it was observed an increasing of the maximum Tc. For the symmetry dx2�����y2 , in the RM approximation, we observe a behavior for Tc as a function of U, similar to that one of the symmetry s, however, in this case the maximum Tc decreases with U. The s extended symmetry presents a di erent behavior for the Tc. The superconductivity occurs in the low occupancy region, in the hole doping regime, and in the region of high occupations, in the electron doping regime. However, when U increases, superconductivity also occurs for occupations close to NT = 1; 0 . A more detailed analysis of the band structure has shown that the increase in the superconducting region when U is increased, is directly linked to the antiferromagnetic correlations, which deform the energy bands. Thus, in general, we can conclude that the antiferromagnetic correlations that cause a pseudogap in the density of states can signi cantly a ect the superconducting critical temperature. |
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Supercondutividade na presença de correlações que podem gerar pseudogapSuperconductivity in the presence o correlations that can generate pseudogapPseudogapFunções de GreenInteração coulombianaModelo de Hubbard de uma bandaSupercondutividadeGreen's functionsCoulomb interactionSuperconductivityHubbard modelCNPQ::CIENCIAS EXATAS E DA TERRA::FISICASince the discovery of superconductivity at high temperatures in 1986, the problem of correlations in superconductivity has received a lot of attention, but it remains as an open problem in condensed matter physics. In this work, superconductivity with di erent symmetries is considered in an one-band Hubbard model. Besides the local repulsive interaction, the studied model also presents an attractive potential, which is responsible for the superconductivity. This study was conducted for superconductors with s, dx2�����y2 , and s-extended symmetry. The main objective is to investigate the role of correlations in the normal and superconducting properties of the model. To treat the model, we used the Green's functions technique together with a n-pole approximation. The n-pole approximation was considered in two versions, the original version (R-O) proposed by Roth (Phys. Rev 184 (1969)) and a modi ed version (R-M) (IJMPB 25 (2011)), which describes most appropriate antiferromagnetic correlations associated with the model. In the R-M version, antiferromagnetic correlations may give rise to a pseudogap in the density of states of the normal state. The pseudogap has been a central point in the study of cuprate superconductors because it is believed to be directly associated with the mechanisms responsible for superconductivity in these systems. More speci cally, we investigated how the correlations responsible for the pseudogap scenario a ect the superconducting critical temperature for the di erent symmetries. The obtained results show that superconductors with di erent symmetries are a ected di erently by the correlations. In general, the critical transition temperature Tc is higher in the R-M approximation compared to that of the R-O approximation. Compared to mean eld results, the Tc 's obtained in the n-pole approximations are higher than the mean eld ones. For s symmetry, in the RM approximation, the increasing of the interaction U, suppresses the superconductivity in the region of occupations close to NT = 1; 0 (with NT < 1; 0) and favors superconductivity in an intermediate region of occupation. In this case, it was observed an increasing of the maximum Tc. For the symmetry dx2�����y2 , in the RM approximation, we observe a behavior for Tc as a function of U, similar to that one of the symmetry s, however, in this case the maximum Tc decreases with U. The s extended symmetry presents a di erent behavior for the Tc. The superconductivity occurs in the low occupancy region, in the hole doping regime, and in the region of high occupations, in the electron doping regime. However, when U increases, superconductivity also occurs for occupations close to NT = 1; 0 . A more detailed analysis of the band structure has shown that the increase in the superconducting region when U is increased, is directly linked to the antiferromagnetic correlations, which deform the energy bands. Thus, in general, we can conclude that the antiferromagnetic correlations that cause a pseudogap in the density of states can signi cantly a ect the superconducting critical temperature.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESDesde a descoberta da supercondutividade em altas temperaturas em 1986, o problema das correlações na supercondutividade tem recebido muita atenção, mas permanece como um problema em aberto na física da matéria condensada. Neste trabalho, considerase supercondutividade com diferentes simetrias em um modelo de Hubbard de uma banda. Além da interação repulsiva local, o modelo estudado apresenta também um potencial atrativo, responsável pela supercondutividade. Este estudo foi realizado para supercondutores com simetria de onda s, dx2y2 e s-estendida. O principal objetivo, é investigar o papel das correlações nas propriedades normais e supercondutoras do modelo. Para tratar o modelo, utilizou-se a técnica das funções de Green em conjunto com uma aproximação de n-polos. Considerou-se a aproximação de n-polos em duas versões, a versão original (R-O) proposta por Roth (Phys. Rev 184 (1969)) e uma versão modi cada (R-M) (IJMPB 25 (2011)), a qual descreve de forma mais adequada as correlações antiferromagnéticas associadas ao modelo. Na versão R-M, as correlações antiferromagnéticas podem dar origem a um pseudogap na densidade de estados do estado normal. O pseudogap tem sido um ponto central no estudo dos supercondutores cupratos, porque acredita-se que o mesmo esteja diretamente associado aos mecanismos responsáveis pela supercondutividade, nesses sistemas. Mais especi camente, investigamos de que forma as correlações responsáveis pelo cenário do pseudogap afetam a temperatura crítica supercondutora para as simetrias de onda s, dx2y2 e s-estendida. Os resultados obtidos mostram que supercondutores com simetrias distintas são afetados de forma diferente, pelas correlações. De forma geral, a temperatura crítica de transição Tc é maior na aproximação R-M quando comparada com a da aproximação R-O. Em comparação com resultados de campo médio, os Tc's obtidos nas aproximações n-polos são maiores do que os de campo médio. Para a simetria s, na aproximação R-M, o aumento da interação coulombiana U suprime a supercondutividade na região de ocupações próximas a NT = 1; 0 (com NT < 1; 0) e favorece a supercondutividade em uma região intermediária de ocupação, inclusive aumentando o Tc máximo. Para a simetria dx2y2 , na aproximação R-M, observa-se um comportamento para o Tc em função de U, parecido ao da simetria s, no entanto, nesse caso o Tc máximo diminui com U. A simetria s-estendida apresenta um comportamento diferente para o Tc em função da ocupação onde a supercondutividade ocorre, na região de baixas ocupações, no regime de dopagem por buracos, e na região de altas ocupações, no regime de dopagem por elétrons. No entanto, quando o U aumenta, a supercondutividade passa a ocorrer também para ocupações próximas a NT = 1; 0. Uma análise mais detalhada da estrutura de bandas mostrou que o aumento da região supercondutora quando U cresce, está diretamente ligado às correlações antiferromagnéticas, as quais deformam as bandas de energia. Assim, podemos concluir que as correlações antiferromagnéticas responsáveis por dar origem a um pseudogap na densidade de estados, podem afetar significativamente a temperatura crítica supercondutora.Universidade Federal de Santa MariaBrasilFísicaUFSMPrograma de Pós-Graduação em FísicaCentro de Ciências Naturais e ExatasCalegari, Eleonir Joãohttp://lattes.cnpq.br/6030572534512173Magalhães, Sergio GarciaLazo, Matheus JatkoskeCarara, Marcos AndréSilva, Leandro Barros daSampaio, Leonardo Fernandes2024-02-06T13:03:50Z2024-02-06T13:03:50Z2019-09-30info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/doctoralThesisapplication/pdfhttp://repositorio.ufsm.br/handle/1/31398porAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/info:eu-repo/semantics/openAccessreponame:Manancial - Repositório Digital da UFSMinstname:Universidade Federal de Santa Maria (UFSM)instacron:UFSM2024-02-06T13:03:50Zoai:repositorio.ufsm.br:1/31398Biblioteca Digital de Teses e Dissertaçõeshttps://repositorio.ufsm.br/ONGhttps://repositorio.ufsm.br/oai/requestatendimento.sib@ufsm.br||tedebc@gmail.comopendoar:2024-02-06T13:03:50Manancial - Repositório Digital da UFSM - Universidade Federal de Santa Maria (UFSM)false |
dc.title.none.fl_str_mv |
Supercondutividade na presença de correlações que podem gerar pseudogap Superconductivity in the presence o correlations that can generate pseudogap |
title |
Supercondutividade na presença de correlações que podem gerar pseudogap |
spellingShingle |
Supercondutividade na presença de correlações que podem gerar pseudogap Sampaio, Leonardo Fernandes Pseudogap Funções de Green Interação coulombiana Modelo de Hubbard de uma banda Supercondutividade Green's functions Coulomb interaction Superconductivity Hubbard model CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA |
title_short |
Supercondutividade na presença de correlações que podem gerar pseudogap |
title_full |
Supercondutividade na presença de correlações que podem gerar pseudogap |
title_fullStr |
Supercondutividade na presença de correlações que podem gerar pseudogap |
title_full_unstemmed |
Supercondutividade na presença de correlações que podem gerar pseudogap |
title_sort |
Supercondutividade na presença de correlações que podem gerar pseudogap |
author |
Sampaio, Leonardo Fernandes |
author_facet |
Sampaio, Leonardo Fernandes |
author_role |
author |
dc.contributor.none.fl_str_mv |
Calegari, Eleonir João http://lattes.cnpq.br/6030572534512173 Magalhães, Sergio Garcia Lazo, Matheus Jatkoske Carara, Marcos André Silva, Leandro Barros da |
dc.contributor.author.fl_str_mv |
Sampaio, Leonardo Fernandes |
dc.subject.por.fl_str_mv |
Pseudogap Funções de Green Interação coulombiana Modelo de Hubbard de uma banda Supercondutividade Green's functions Coulomb interaction Superconductivity Hubbard model CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA |
topic |
Pseudogap Funções de Green Interação coulombiana Modelo de Hubbard de uma banda Supercondutividade Green's functions Coulomb interaction Superconductivity Hubbard model CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA |
description |
Since the discovery of superconductivity at high temperatures in 1986, the problem of correlations in superconductivity has received a lot of attention, but it remains as an open problem in condensed matter physics. In this work, superconductivity with di erent symmetries is considered in an one-band Hubbard model. Besides the local repulsive interaction, the studied model also presents an attractive potential, which is responsible for the superconductivity. This study was conducted for superconductors with s, dx2�����y2 , and s-extended symmetry. The main objective is to investigate the role of correlations in the normal and superconducting properties of the model. To treat the model, we used the Green's functions technique together with a n-pole approximation. The n-pole approximation was considered in two versions, the original version (R-O) proposed by Roth (Phys. Rev 184 (1969)) and a modi ed version (R-M) (IJMPB 25 (2011)), which describes most appropriate antiferromagnetic correlations associated with the model. In the R-M version, antiferromagnetic correlations may give rise to a pseudogap in the density of states of the normal state. The pseudogap has been a central point in the study of cuprate superconductors because it is believed to be directly associated with the mechanisms responsible for superconductivity in these systems. More speci cally, we investigated how the correlations responsible for the pseudogap scenario a ect the superconducting critical temperature for the di erent symmetries. The obtained results show that superconductors with di erent symmetries are a ected di erently by the correlations. In general, the critical transition temperature Tc is higher in the R-M approximation compared to that of the R-O approximation. Compared to mean eld results, the Tc 's obtained in the n-pole approximations are higher than the mean eld ones. For s symmetry, in the RM approximation, the increasing of the interaction U, suppresses the superconductivity in the region of occupations close to NT = 1; 0 (with NT < 1; 0) and favors superconductivity in an intermediate region of occupation. In this case, it was observed an increasing of the maximum Tc. For the symmetry dx2�����y2 , in the RM approximation, we observe a behavior for Tc as a function of U, similar to that one of the symmetry s, however, in this case the maximum Tc decreases with U. The s extended symmetry presents a di erent behavior for the Tc. The superconductivity occurs in the low occupancy region, in the hole doping regime, and in the region of high occupations, in the electron doping regime. However, when U increases, superconductivity also occurs for occupations close to NT = 1; 0 . A more detailed analysis of the band structure has shown that the increase in the superconducting region when U is increased, is directly linked to the antiferromagnetic correlations, which deform the energy bands. Thus, in general, we can conclude that the antiferromagnetic correlations that cause a pseudogap in the density of states can signi cantly a ect the superconducting critical temperature. |
publishDate |
2019 |
dc.date.none.fl_str_mv |
2019-09-30 2024-02-06T13:03:50Z 2024-02-06T13:03:50Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/doctoralThesis |
format |
doctoralThesis |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://repositorio.ufsm.br/handle/1/31398 |
url |
http://repositorio.ufsm.br/handle/1/31398 |
dc.language.iso.fl_str_mv |
por |
language |
por |
dc.rights.driver.fl_str_mv |
Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/ info:eu-repo/semantics/openAccess |
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Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/ |
eu_rights_str_mv |
openAccess |
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application/pdf |
dc.publisher.none.fl_str_mv |
Universidade Federal de Santa Maria Brasil Física UFSM Programa de Pós-Graduação em Física Centro de Ciências Naturais e Exatas |
publisher.none.fl_str_mv |
Universidade Federal de Santa Maria Brasil Física UFSM Programa de Pós-Graduação em Física Centro de Ciências Naturais e Exatas |
dc.source.none.fl_str_mv |
reponame:Manancial - Repositório Digital da UFSM instname:Universidade Federal de Santa Maria (UFSM) instacron:UFSM |
instname_str |
Universidade Federal de Santa Maria (UFSM) |
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UFSM |
institution |
UFSM |
reponame_str |
Manancial - Repositório Digital da UFSM |
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Manancial - Repositório Digital da UFSM |
repository.name.fl_str_mv |
Manancial - Repositório Digital da UFSM - Universidade Federal de Santa Maria (UFSM) |
repository.mail.fl_str_mv |
atendimento.sib@ufsm.br||tedebc@gmail.com |
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1805922044701835264 |