### Browsing by Author "Ramos, J. A. P."

Now showing 1 - 4 of 4

###### Results Per Page

###### Sort Options

Item Dynamical transitions and sliding friction of the phase-field-crystal model with pinning(American Physical Society (APS), 2010) Ramos, J. A. P.; Granato, E.; Ying, S. C.; Achim, C. V.; Elder, K. R.; Ala-Nissilä, Tapio; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe study the nonlinear driven response and sliding friction behavior of the phase-field-crystal (PFC) model with pinning including both thermal fluctuations and inertial effects. The model provides a continuous description of adsorbed layers on a substrate under the action of an external driving force at finite temperatures, allowing for both elastic and plastic deformations. We derive general stochastic dynamical equations for the particle and momentum densities including both thermal fluctuations and inertial effects. The resulting coupled equations for the PFC model are studied numerically. At sufficiently low temperatures, we find that the velocity response of an initially pinned commensurate layer shows hysteresis with dynamical melting and freezing transitions for increasing and decreasing applied forces at different critical values. The main features of the nonlinear response in the PFC model are similar to the results obtained previously with molecular dynamics simulations of particle models for adsorbed layers.Item Glassy phases and driven response of the phase-field-crystal model with random pinning(American Physical Society (APS), 2011) Granato, E.; Ramos, J. A. P.; Achim, C. V.; Lehikoinen, J.; Ying, S. C.; Ala-Nissilä, Tapio; Elder, K. R.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe study the structural correlations and the nonlinear response to a driving force of a two-dimensional phase-field-crystal model with random pinning. The model provides an effective continuous description of lattice systems in the presence of disordered external pinning centers, allowing for both elastic and plastic deformations. We find that the phase-field crystal with disorder assumes an amorphous glassy ground state, with only short-ranged positional and orientational correlations, even in the limit of weak disorder. Under increasing driving force, the pinned amorphous-glass phase evolves into a moving plastic-flow phase and then, finally, a moving smectic phase. The transverse response of the moving smectic phase shows a vanishing transverse critical force for increasing system sizes.Item Nonlinear driven response of a phase-field crystal in a periodic pinning potential(American Physical Society (APS), 2009) Achim, C. V.; Ramos, J. A. P.; Karttunen, M.; Elder, K. R.; Granato, E.; Ala-Nissilä, Tapio; Ying, S. C.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe study numerically the phase diagram and the response under a driving force of the phase field crystal model for pinned lattice systems introduced recently for both one- and two-dimensional systems. The model describes the lattice system as a continuous density field in the presence of a periodic pinning potential, allowing for both elastic and plastic deformations of the lattice. We first present results for phase diagrams of the model in the absence of a driving force. The nonlinear response to a driving force on an initially pinned commensurate phase is then studied via overdamped dynamic equations of motion for different values of mismatch and pinning strengths. For large pinning strength the driven depinning transitions are continuous, and the sliding velocity varies with the force from the threshold with power-law exponents in agreement with analytical predictions. Transverse depinning transitions in the moving state are also found in two dimensions. Surprisingly, for sufficiently weak pinning potential we find a discontinuous depinning transition with hysteresis even in one dimension under overdamped dynamics. We also characterize structural changes of the system in some detail close to the depinning transition.Item Thermal fluctuations and phase diagrams of the phase-field crystal model with pinning(American Physical Society (APS), 2008) Ramos, J. A. P.; Granato, E.; Achim, C. V.; Ying, S. C.; Elder, K. R.; Ala-Nissilä, Tapio; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe study the influence of thermal fluctuations in the phase diagram of a recently introduced two-dimensional phase field crystal model with an external pinning potential. The model provides a continuum description of pinned lattice systems allowing for both elastic deformations and topological defects. We introduce a nonconserved version of the model and determine the ground-state phase diagram as a function of lattice mismatch and strength of the pinning potential. Monte Carlo simulations are used to determine the phase diagram as a function of temperature near commensurate phases. The results show a rich phase diagram with commensurate, incommensurate, and liquidlike phases with a topology strongly dependent on the type of ordered structure. A finite-size scaling analysis of the melting transition for the c(2×2) commensurate phase shows that the thermal correlation length exponent ν and specific heat behavior are consistent with the Ising universality class as expected from analytical arguments.