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Master's Dissertation
DOI
10.11606/D.76.1995.tde-11092008-165010
Document
Author
Full name
Sandra Cristina Costa
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1995
Supervisor
Committee
Libero, Valter Luiz (President)
Ioriatti Junior, Liderio Citrangulo
Yoshida, Makoto
Title in Portuguese
Calor específico do modelo de Anderson de uma impureza por grupo de renormalização numérico
Keywords in Portuguese
Discretização logarítmica.
Efeito Kondo
Ligas magnéticas
Magnetização
Modelo de Anderson
Abstract in Portuguese
Neste trabalho, calculam-se o calor específico e a entropia do Modelo de Anderson simétrico de uma impureza usando o Grupo de Renormalização Numérico (GRN). O método é baseado na discretização logarítmica da banda de condução do metal hospedeiro a qual a impureza está acoplada. Porém, esta discretização introduz oscilações nas propriedades termodinâmicas. Esta inconveniência, inerente ao método, é contornável para a suscetibilidade magnética, mas é crítica para o calor específico, restringindo o alcance do GRN. Para sobrepor essa dificuldade, é usado o novo procedimento denominado intercalado que foi desenvolvido para o cálculo da suscetibilidade magnética de modelos de duas impurezas. Para reduzir as matrizes e o tempo computacional, é usado, também, o operador carga axial, recentemente definido no contexto do Modelo de Kondo de duas impurezas, e que é conservado pelo Hamiltoniano de Anderson simétrico. As curvas obtidas são comparadas com resultados exatos obtidos por ansatz de Bethe e pelo Modelo de Nível Ressonante.
Title in English
Numerical Renormalization-group Computation of Specific Heats.
Keywords in English
Kondo efect
Logarithmic discretization
Magnetic alloys
Magnetization
Modelo de Anderson
Abstract in English
The specific heat and the entropy of the one-impurity symmetric Anderson Model are calculated using the Numerical Renormalization Group (NRG). The heart of the method is the logarithmic discretization of the metal conduction band where the impurity is coupled. However, this discretization, inherent in the method, introduces oscillations in the thermodynamical properties. For the susceptibility it is not so critical but for the specific heat the usual calculation is prohibitive. To overcome this difficulty, we use the new procedure called interleaved that was developed to calculate the susceptibility of two-impurity models. In order to reduce the matrices and computation time, use is made of the axial charge operator recently defined in the two-impurity Kondo Model context and that is conserved by the symmetric Anderson Hamiltonian. The curves obtained are compared with exacts results of Bethe ansatz and Resonant Level Model.
 
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SandraCostaM.pdf (2.18 Mbytes)
Publishing Date
2008-09-15
 
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