Superdomain dynamics in ferroelectric-ferroelastic films: switching, jamming, and relaxation

Recent experimental work shows that ferroelectric switching can occur in large jumps in which ferroelastic superdomains switch together, rather than having the numerous smaller ferroelectric domains switch within them. In this sense the superdomains play a role analogous to that of Abrikosov vortices in thin superconductorsing films under the Kosterlitz-Thouless framework, which control the dynamics more than individual Cooper pairs within them do. Here we examine the dynamics of ferroelastic superdomains in ferroelastic ferroelectrics and their role in switching devices such as memories. Jamming of ferroelectric domains in thin films has revealed an unexpected time dependence of t^-1/4 at long times (hours), but it is difficult to discriminate between power-law and exponential relaxation. Other aspects of that work, including spatial period doubling of domains, led to a description of ferroelastic domains as nonlinear processes in a viscoelastic medium which produce folding and metastable kinetically limited states. This ¼ exponent is a surprising agreement with the well-known value of ¼ for coarsening dynamics in viscoelastic media. We try to establish a link between these two processes, hitherto considered unrelated, and with superdomains and domain bundles. We note also that high-Tc superconductors share many of the ferroelastic domain properties discussed here and that several new solar cell materials and metal-insulator transition systems are ferroelastic.