Topological phase transitions in perovskite superlattices driven by temperature, electric field, and doping

Many dipolar topological structures have been experimentally demonstrated on ${({\mathrm{PbTiO}}_{3})}_{n}/{({\mathrm{SrTiO}}_{3})}_{n}$ superlattices, such as flux closure, vortex, and skyrmion. In this work, we employ deep potential molecular dynamics (MD) to investigate the atomic-level dynamical response of the ${({\mathrm{PbTiO}}_{3})}_{10}/{({\mathrm{SrTiO}}_{3})}_{10}$ superlattice, which hosts polar vortex arrays, to variations in temperature and electric field. Our simulations reveal a unique phase transition sequence from ferroelectric-like to antiferroelectric-like to paraelectric in the in-plane direction as temperature increases. In the ferroelectric-like state, we observe field-driven reversible switching of in-plane polarization coupled with out-of-plane movements of vortex cores. In the antiferroelectric-like region, the polarization-electric field hysteresis loop exhibits a superparaelectric feature, showing nearly no loss. This behavior is attributed to a strong recovering force that drives the formation of polar vortex arrays, dictated by the electrical and mechanical boundary conditions within the superlattice. The ${({\mathrm{PbTiO}}_{3})}_{10}/{{(\mathrm{SrTiO}}_{3})}_{10}$ superlattice in the antiferroelectric-like state also demonstrates large in-plane susceptibility and tunability. The effect of Pb doping in the ${\mathrm{SrTiO}}_{3}$ layer on the topological structural transition in the superlattice is investigated. The weakened depolarization field in the ${\mathrm{PbTiO}}_{3}$ layers leads to new dipolar configurations, such as an enlarged skyrmion bubble within $c$ domains in ${({\mathrm{PbTiO}}_{3})}_{10}/{({\mathrm{Pb}}_{0.4}{\mathrm{Sr}}_{0.6}{\mathrm{TiO}}_{3})}_{10}$, and we quantify their thermal and electrical responses using MD simulations. These quantitative atomistic insights will be useful for the controlled optimization of perovskite superlattices for various device applications.