Towards Resolving Landauer's Paradox Through Direct Observation of Multiscale Ferroelastic-Ferroelectric Interplay

Abstract: Electric-polarization reversibility in nano-ferroelectric structures renders them as a convenient platform for exploring phase transitions and developing energy-efficient switching devices. However, the fundamental question of how ferroic domains switch, i.e. how the polarization changes from one state to another, is yet to be answered fully. There are contradicting models and a wide body of accumulated data which disagree as to whether the switching requires domain nucleation. Moreover, ferroelectric domains switch under electric fields that are supposedly too weak to form nucleation sites, indicating that the level of disorder seen in real systems plays an important role. This longstanding so-called Landauer's paradox is the ferroelectric equivalent to the absence of raindrop formation in a dust-free vacuum, leading to supersaturated vapors that cannot exist otherwise, e.g. in spinodal decompositions or inhomogeneous nucleation environments. Here we show that polarization switching in ferroelectric-ferroelastic systems comprises domain types that differ by symmetry, lengthscale and switching energy. These domains switch simultaneously thanks to intermediate-range order of organized pinning sites, supporting the previously-unexplained coexistence of nucleation-and-growth and nucleation-frustrated mechanisms. Our treatment is applicable to other Kolmogorov-Avrami systems with multi-scale phase transitions. Finally, we demonstrate augmented electromechanical coupling based on the collective motion of pinning sites, which is promising for nano electro-mechanical and low-power switching devices.