Séminaire de groupe
|Phase transitions and ordering dynamics in 2d spin-ice|
|LPTHE, Paris VI Jussieu|
|lundi 05 décembre 2011 , 10h25|
|Salle de séminaire du groupe de Physique Statistique|
Spin-ice is the magnetic analog of Pauling's water ice which constitutes the prototypical example of geometrical frustration. This type of materials provides a variety of novel states, one of the most surprising ones is the emergence of de-confined magnetic monopoles as thermal excitations. They provide concrete experimental realization of vertex models that have been extensively studied theoretically. I introduce a general 2D vertex model on a square lattice to study the dynamics of this kind of systems. It is a generalization of the extensively studied six- and eight-vertex models, which are integrable. Before discussing dynamical aspects, I shall present the equilibrium phase diagram of our model. The phases of the system and the nature of the phase transitions are radically modified by allowing defects, i.e. breaking the integrability of the six-vertex model. Once the equilibrium phases have been identified, we study the phase ordering dynamics of the 2D spin-ice model following a quench from a disordered initial condition into its paramagnetic (close to a quasi long-range order), ferromagnetic and antiferromagnetic phases. We analyze the evolution of the density of topological defects and we show that these take finite density over very long periods of time in all kind of quenches. We identify the leading mechanisms involved in the ordering process, involving the growth of domains and we evaluate the (anisotropically) growing lengths involved in dynamical scaling.