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

JY Yang and S Liu, PHYSICAL REVIEW B, 110, 214112 (2024).

DOI: 10.1103/PhysRevB.110.214112

Many dipolar topological structures have been experimentally demonstrated on (PbTiO3)n/(SrTiO3)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 (PbTiO3)10/(SrTiO3)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 (PbTiO3)10/(SrTiO3)10 superlattice in the antiferroelectric-like state also demonstrates large in-plane susceptibility and tunability. The effect of Pb doping in the SrTiO3 layer on the topological structural transition in the superlattice is investigated. The weakened depolarization field in the PbTiO3 layers leads to new dipolar configurations, such as an enlarged skyrmion bubble within c domains in (PbTiO3)10/(Pb0.4Sr0.6TiO3)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.

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