Emergent Antipolar Phase in BiFeO₃–La_0.7Sr_0.3MnO₃ Superlattice

Abstract

Ferroelectric–paraelectric\nsuperlattices show emerging new\nstates, such as polar vortices, through the interplay and different\nenergy scales of various thermodynamic constraints. By introducing\nmagnetic coupling at BiFeO₃–La_0.7Sr_0.3MnO₃ interfaces epitaxially grown on SrTiO₃ substrate, we find, for the first time in thin films, a sub-nanometer\nthick lamella-like BiFeO₃. The emergent phase is characterized\nby an arrangement of a two unit cell thick lamella-like structure\nfeaturing antiparallel polarization, resulting an antiferroelectric-like\nstructure typically associated with a morphotropic phase transition.\nThe antipolar phase is embedded within a nominal <i>R</i>3<i>c</i> structure and is independent of the BiFeO₃ thickness (4–30 unit cells). Moreover, the superlattice\nstructure with the morphotropic phase demonstrates azimuth-independent\nsecond harmonic generation responses, indicating a change of overall\nsymmetry mediated by a delicate spatial distribution of the emergent\nphase. This work enriches the understanding of a metastable state\nmanipulated by thermodynamic constraints by lattice strain and magnetic\ncoupling.