Transições de primeira ordem no modelo vidro de spin ising fermiônico em um campo transverso

• Autor(a) principal: Morais Junior, Carlos Alberto Vaz de
• Data de Publicação: 2006
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Manancial - Repositório Digital da UFSM
• dARK ID: ark:/26339/0013000013mtq
• Texto Completo: http://repositorio.ufsm.br/handle/1/9201
• topic: Flutuações de carga; Flutuações quânticas; Condições de estabilidade; Ponto tricrítico; Charge fluctuations; Quantum fluctuations; Stability conditions; Tricritical point; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

The present work analyzes the fermionic Ising spin glass model in a transverse magnetic field. The problem is written in the Grand Canonical ensemble with the spin operators represented by bilinear combinations of fermionic fields. The transverse field is a spin "flip" mechanism and inserts quantum fluctuations, which can lead the transition temperature Tj to quantum critical point (QCP). In this case, the phase transition from spin glass to paramagnetic phases occurs in T = o. On the other hand, charge fluctuations controlled by chemical potentiall-L show the existence of a tricritical point. The replica method with replica symmetry and static approximation are used to solve this problem. However, the replica symmetry solution shows some problems, like negative entropy in low temperatures. Thus, the stability conditions are derived to test the generated solution of this IDodel. The main purpose of this work is to study the competition between spin glass and paramagnetic phases with both quantum and charge fluctuations. After the stability conditions are derived, a detailed sight into the generated solution is shown under the form of diagrams phase. The stability conditions, however, show another applications in the present problem, once they can be used, for instance, in the tricritical point derivation.