Estruturas, modos normais e difusão em um sistema periódico quasi-unidimensional

• Autor(a) principal: Carvalho, João Cláudio Nunes
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Ceará (UFC)
• Texto Completo: http://www.repositorio.ufc.br/handle/riufc/7705
• topic: Sistema quasi-unidimensional; Potencial periódico; Partículas de Yukawa; Difusão

In this thesis we analyze the structural properties and diffusive dynamics for a classical system of two-dimensional (2D) charged particles, interacting through a repulsive Yukawa potential of the type exp(−r/ lambda)/r, and confined in a parabolic channel that limits the movement of particles in the y direction. Along the x direction, the particles are subject to a periodic potential. The ground-state configurations and the normal mode spectra are obtained in terms of the periodicity (L), the intensity of the periodic potential (V0) and density. An interesting set of tunable ground-state configurations are found, with first- or second-order structural transitions between them. A configuration with particles aligned, perpendicular to the x direction, in each minimum of the periodic potential is obtained for V0 larger than some critical value that has a power-law dependence on the density. The phonon spectrum of different configurations was also calculated. A localization of the modes into a small frequency interval is observed for sufficiently large strength of the periodic potential, and a tunable gap in the phonon spectrum is found as a function of V0. Langevin dynamic simulations are used to investigate the effect of the particle density, the amplitude of the periodic substrate, and the range of the interparticle interaction potential on the diffusive behavior of the particles. We found that in general the diffusion is suppressed with increasing amplitude of the periodic potential, but for specific values of the strength of the substrate potential a remarkably increase of the diffusion is found with increasing periodic potential amplitude. In addition, we found a strong dependence of the diffusion on the specific arrangement of the particles, e.g. singlechain versus multi-chain configuration. For certain particle configurations, a reentrant behavior of the diffusion is found as function of the substrate strength due to structural transitions in the ordering of the particles.