Self-organization and criticality in martensite
Facultat de Física, Aula Pere Pascual, planta 6
A martensitic phase-transformation is a first-order diffusionless transition occurring in elastic crystals and characterized by an abrupt change of shape of the underlying crystal lattice. It is the basic activation mechanism for the Shape-Memory effect. In this talk we present a probabilistic model for the description of martensitic microstructure as an avalanche process. Our approach to the analysis of the model is based on an associated general branching random walk process. Comparisons are reported for numerical and analytical solutions and experimental observations.
Deliberate exotic magnetism via frustration and topology
Aula Eduard Fontseré - Facultat de Física UB
So called "Artificial Spin Ices" are two dimensional arrays of magnetic, interacting nanostructures whose geometry can be chosen at will, and whose elementary degrees of freedom can be characterized directly. They were introduced at first to study frustration in a controllable setting, to mimic the behavior of spin ice, rare heart pyrochlores, but at more useful temperature and field ranges and with direct characterization, and to provide practical implementation to celebrated, exactly solvable models of statistical mechanics previously devised to gain understanding of degenerate ensembles. With the evolution of nano fabrication and of experimental protocols it is now possible to characterize the material in real-time, real-space, and to realize virtually any geometry, for direct control over the collective dynamics. This has recently opened a path toward the deliberate design of novel, exotic states, not found in natural materials. We will provide an introduction to the material, the early works, and then, by reporting on more recent results, we will proceed to describe directions, which includes the design of desired topologically protected states and their implications to kinetics.