Domain dynamics in low strain BaTiO3 thin films

Phase transitions dynamics and pre-equilibrium phenomena are difficult to detect, raising questions about the relative role of kinetics versus thermodynamics in the final ordered state. Ferroic materials are good examples of symmetry breaking phase transitions. In particular, ferroelastic layers under epitaxial strain minimize the elastic energy by forming periodically ordered domains. We have directly observed that the equilibrium domain structure in these materials is achieved by halving of the domain periodicity, sequentially and multiple times. The process is reversible, displaying periodicity doubling as the temperature is increased. The resulting periodicity halving/doubling cascades follow a 2ⁿ size-scaling (kinetic) law that, combined with the thermodynamic limit (Roytburd law), yields the actual domain size. These behaviour shows the universality of the "edge of chaos" formalism (by which oscillatory systems are known to go through period-doubling cascades before reaching the chaotic dynamical regime) applies to spatially periodic patterns. It does provide an experimental link between maximum adaptability that is believed to take pace at the "edge of chaos" and maximum susceptibilty at order-disorder phase transitions. Implications for adaptable electronics and neuromorphic computing will be discussed.