Seminar: Phase transitions and dynamics of bidimensional systems with isotropic competing interactions

Dr. Lucas Nicolao
Dipartimento di Fisica
Sapienza - Università di Roma

I'll present some results of 2D isotropic systems presenting modulated phases, constituted basically of stripes and bubbles, modeled by a simple ferromagnetic Ginzburg-Landau Hamiltonian with an isotropic long-range repulsive interaction using Langevin dynamics.
In the first part of the seminar I'll introduce the simulation method for the Langevin dynamics and show that this system undergoes a phase transition from a labyrinthic phase to a low temperature nematic phase that is characterized by having no translational order, only orientational order between the stripes. Later I'll present results where we are able to follow the asymptotic dynamics both analytically, through a mean-field approximation, and numerically.
Both approaches agree on the value of the upper-critical field, that distinguishes the ferromagnetic and bubble phases.
Surprisingly, the predicted simple aging at zero field is observed in the simulations, where a logarithmic growth is found in contrast with the predicted power-law growth.

April 12, 2012 at 14:00 in the IENI meeting room