Intrinsic local modes and heterogeneity in relaxor ferroelectrics

We suggest that ferroelectric relaxor glasses represent an important class of materials in which intrinsic spatial heterogeneity and multiscale dynamics can arise from the formation of local modes due to inherent nonlinearity in the polarizable medium. Specifically, the phenomenology of relaxor ferroelectrics in terms of the spherical random bond-random field (Blinc et al 1999 Phys. Rev. Lett. 83 424) model is explained microscopically by the formation of discrete breathers embedded in a soft but silent medium, which form in-gap local modes (IGLM) where charge and lattice are intrinsically coupled. Complete mode softening is inhibited by the IGLM and soft elasticity a prerequisite for their existence.