Wannier-Based Definition of Layer Polarizations in Perovskite Superlattices

In insulators, the method of Marzari and Vanderbilt [Phys. Rev. B 56, 12 847 (1997)] can be used to generate maximally localized Wannier functions whose centers are related to the electronic polarization. In the case of layered insulators, this approach can be adapted to provide a natural definition of the local polarization associated with each layer, based on the locations of the nuclear charges and one-dimensional Wannier centers comprising each layer. Here, we use this approach to compute and analyze layer polarizations of ferroelectric perovskite superlattices, including changes in layer polarizations induced by sublattice displacements (i.e., layer-decomposed Born effective charges) and local symmetry breaking at the interfaces. The method provides a powerful tool for analyzing the polarization-related properties of complex layered oxide systems.

Figure 1

Dispersion of WF center positions for a 1BT/1ST superlattice as a function of $\mathbf{g}=(k_x,k_y)$.

Figure 2

Local polarization profile of 1ST/2BT supercell, from effective charge approximation based on $A$ centered (open square) or $B$ centered (open diamonds) analysis, and from layer polarization analysis (filled circles). The overall supercell polarization is $0.22\mathrm{C}/{\mathrm{m}}^2$.

Figure 3

Layer polarization as a function of (a) total polarization of the supercell, and (b) macroscopic electric field in the supercell, for six consecutive layers in the 1ST/2BT supercell. Labeling of layers follows Fig. 1.