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Doctoral Thesis
DOI
10.11606/T.97.2008.tde-20082013-163321
Document
Author
Full name
Mário Sérgio da Luz
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Lorena, 2008
Supervisor
Committee
Santos, Carlos Alberto Moreira dos (President)
Granato, Enzo
Kopelevitch, Iakov Veniaminovitch
Nunes, Cristina Bórmio
Shigue, Carlos Yujiro
Title in Portuguese
Efeito Hall em supercondutores a campo magnético nulo
Keywords in Portuguese
Efeito Hall
Granularidade
Materiais anisotropicos
Supercondutividade
Abstract in Portuguese
Este trabalho reporta a influencia da granularidade sobre a resistencia transversal em funcao da temperatura, RXY(T), medidas em amostras policristalinas dos sistemas supercondutores Bi2Sr2Ca-1-xPrxCu2O8+??e YBa2Cu3O7-?, e em monocristais de composicao Li0,9Mo6O17. Foi observada tensao nao nula na voltagem Hall, em campo magnetico aplicado nulo, nas proximidades da temperatura de transicao supercondutora (TC), para os tres sistemas em questao. A tensao Hall a campo zero se manifesta atraves de picos abaixo de TC, que esta relacionada com a componente longitudinal da resistencia e, por consequencia, com o carater granular das amostras. E apresentada tambem a existencia de uma assimetria no sinal Hall em campo magnetico aplicado. Estes comportamentos sao discutidos baseado no movimento de vortices e anti-vortices, de Josephson e Abrikosov no interior das amostras. Para monocristais de Li0,9Mo6O17 tambem foi observado efeito Hall a campo magnetico nulo. Alem do mais, uma nova relacao de anisotropia confirma o carater qause-unidmensional deste composto, mas mostra uma anisotropia menor do que aquela reportada previamente. Foi observado tambem que este material apresenta transicoes do tipo supercondutor-isolante (SIT) e metal- isolante (MIT) em temperaturas proximas ao zero absoluto.
Title in English
Hall Effect in Superconductors at Zero Magnetic Field
Keywords in English
Anisotropic Materials
Granularity
Hall Effect
Superconductivity
Abstract in English
This work reports the influence of the granularity on the transverse resistance as a function of temperature, RXY(T), in Bi2Sr2Ca1-xPrxCu2O8+??and YBa2Cu3O7-??polycrystalline samples, and Li0.9Mo6O17 single crystals. The effects of warming rate, temperature, applied magnetic field, and electrical current on the Hall resistance are reported. At zero magnetic field two peaks are observed in RXY(T) curves for the three compounds. The peaks are related to the double superconducting transition in the longitudinal component RXX(T) curves. In the superconducting and normal states no transverse voltage has been detected at zero magnetic field, as expected. The results are discussed within the framework of the motion of Abrikosov and Josephson vortices and anti-vortices. A new scaling relation between transverse and longitudinal voltages given by RXY ~ dRXX/dT has been confirmed. Regarding Li0.9Mo6O17 single crystals, Hall resistance at zero applied magnetic field was also observed. Furthermore, the results confirm the quasi-unidimensionality but show smaller anisotropic ratio than previously reported. Simultaneously, the result reveals that the Li0.9Mo6O17 is the first bulk superconducting compound exhibiting superconductor-insulator-transition (SIT) and metal-insulator-transition (MIT) behaviors.
 
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Publishing Date
2013-08-20
 
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