Melting of crystals of polarization vortices and chiral phase transitions in oxide superlattices
Fernando Gómez‐Ortiz, Pablo García‐Fernández, J.M. López, Javier Junquera
Abstract
We study the equilibrium arrangements of polarization vortices in (${\mathrm{PbTiO}}_{3}{)}_{n}/({\mathrm{SrTiO}}_{3}{)}_{n}$ superlattices by means of second-principles simulations. We find that, at low temperatures, polarization vortices organize in a regular arrangement in which clockwise and counterclockwise vortices alternate positions, leading to a crystal-like structure with well-defined handedness. This chiral crystal melts at a critical temperature ${T}_{\mathrm{M}}$ into a chiral liquid where long-range order is lost but handedness is preserved. At even higher temperatures ${T}_{\mathrm{C}}$, a second phase transition occurs at which the chiral liquid of polarization vortices loses its handedness. Both phase transitions can be readily identified by the adequate choices of order parameters.