Estrutura, modos normais e "melting" de um sistema binário de partículas carregadas confinadas em um potencial parabólico

• Ano de defesa: 2005
• Autor(a) principal: Munarin, Felipe de Freitas
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Partículas confinadas; Potencial parabólico; Sistema binário de partículas; Física da matéria condensada; Método de Monte Carlo; Termodinâmica
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/8065

We analyze in this work the structural, dynamical, and thermal properties of a twodimensional system with two types of particles with different charges and/or masses. The charged particles interact through a Coulomb potential and are kept together in a finite region of the plane by a parabolic confinement potential. The structure of the ground state configuration, as well as the normal mode spectrum, are analyzed as a function of the ratio between charges and the ratio between masses of the two types of particles. In general, we show that there is a natural segregation of the distinct particles for critical values of the ratio between charges (masses). However, asymmetrical mixed configurations are also obtained. A very large number of stable configurations is obtained when the ratio between charges is equal, or approximately equal to, the ratio between masses of the different type of particles. The coupling between electrical and inertial properties of the system plays an important role in the critical temperature in which the system presents a solid-liquid phase transition. The normal mode spectrum is carefully analyzed. In particular, the lowest non-zero frequency, which is associated to the stability and deformability of the ground state configuration, is extensively studied as a function of the ratio between charges (masses) of the particles. It is found that a particular ground state configuration may present different normal modes, associated to the lowest non-zero frequency, according to the ratio between the charges (masses) of the particles. The degree of mixing of the two types of particles is summarized in phase diagram. Structural phase transitions from a mixed configuration to the one where the distinct types of particles are separated in different shells are observed. We find that the order of the structural phase transition is also determined by the ratio between charges and masses. A like-order parameter, which characterizes the configuration of the cluster, is defined. Finally, the solid-liquid transition is studied. In general, we find that ground state configurations with magic numbers of particles, presents a high melting temperature. In addition, a very interesting re-entrant effect is presented.