Sommaire:

In geometrically frustrated magnets, the tendency to order locally is hampered by some structural restriction which gives rise to a macroscopic degeneracy of the ground state. This leads to interesting collective phenomena such as `frozen-to-critical' phase transitions, long range correlations and slow dynamics. In this talk I will focus on a paradigmatic system presenting these features: spin-ice in the square lattice. Very recently, artificial spin-ice samples have been realised by nano-lithography. They provide concrete experimental realisations of vertex models of statistical mechanics (among them the integrable six- and eight-vertex models). I will introduce a stochastic extension of the six-vertex model in order to study this kind of system both by numerical and analytical methods. Then, I shall discuss the equilibrium phase diagram of the model and compare our theoretical results with experimental measurements done in `a-thermal' artificial spin-ice samples. The vertex model reproduces the experimental data when we identify the canonical temperature of our model with the configurational Edwards temperature of the samples. The dynamics of artificial spin ice opens the way to access the motion of topological defects in two dimensions. If time allows it, I will also discuss the slow relaxation dynamics of the system following different quenches.

Pour plus d'informations, merci de contacter Berthier L.