Dynamics and phase transitions in lattice systems

Abstract

Systems that tend to develop periodic patterns often display very intriguing phenomena resulting from the competition between external force, elasticity and the periodicity of the structure. The periodicity allows the nucleation of topological defects, like domain walls and dislocations, which determine the dynamical behavior and the mechanisms for phase transitions in the system. Vortex lattices in high-temperature superconducting materials are important examples of this class of systems, due to the great scientific and technological interest in theses materials. In particular, understanding the mechanisms for lattice pinning is of great importance to reach high critical currents in presence of an applied magnetic field and in the development of superconducting devices. Other important examples occur in crystalline surfaces like, growth of strained epitaxial layers and sliding friction in boundary lubrication. In this case, the relevant lattice system consists of many superposed atomic layers under the action of an external force induced by the substrate or another surface. Studies of the dynamics of these systems, allows a better understanding of the ordering and nucleation mechanisms of topological defects that are useful in the fabrication of semiconductor super-lattices. Likewise, studies of siding friction of lubricated surfaces are of great importance for nanotribology. The goal of the project is to develop theoretical research on the dynamics and phase transitions in theses systems. The problems to be investigated and the theoretical methods used are common to the fields, superconductivity and surface Physics, thus allowing for a unified approach to the relevant physical mechanisms. Numerical methods of Monte Carlo and molecular-dynamics simulations will be used in the studies of the relevant models. Important computational limitations like, long execution times due to the slow relaxation and disordered nature of the system phases, should be overcome by the use of parallel processing in a cluster of microcomputers. Among the problems to be investigated are: vortex lattice melting in superconductors, sliding friction and defect nucleation in surfaces. (AU)