Topological polaron in lead titanate

Polaron is a composite quasiparticle [1] in polar semiconductors and insulators [2], influencing many physical properties such as transport and optics. However, first-principles simulations of large polarons in realistic materials have only recently become possible through the ab initio polaron equations [3], which overcome formidable computational costs posed by supercells and self-interaction errors of DFT. This advancement paves the way for exploring novel phenomena and applications based on polaron physics [4,5].

One of the surprising examples is the identification of topological polarons in halide perovskite [6], where the lattice polarizations of large polarons are found to be the counterparts of Bloch points in magnetic structures. This identification is made possible when the simulation cell scales up to millions of atoms. In this presentation, we offer another example of topological polaron in lead titanate (PbTiO3, PTO). PTO is a well-known functional compound for its ferroelectricity, piezoelectricity, and its role as a building block of oxide nanostructures hosting topological states. We will analyze both the electronic and lattice degrees of freedom in the polaron formation in PTO, discuss the mechanism and characteristic numbers of the real-space lattice polarizations, and make connections with experimental measurements.

References:

[1] PRL 129, 076402 (2022)

[2] Nat. Rev. Mat. 6, 560–586 (2021)

[3] PRB 99, 235139 (2019); PRL 122, 246403 (2019)

[4] Nat. Phys. 19, 629–636 (2023)

[5] PRL 132, 036902 (2024)

[6] PNAS 121 (21) e2318151121 (2024)