Electronic structure of twin wall/surface intersections in CaTiO₃ (001)

Domain wall engineering of functional oxides provides a new paradigm for post-CMOS electronics [1]. Domain walls are potentially the perfect structural discontinuity, maintaining the crystalline phase but defining a change in the functional order parameter.
In CaTiO₃ the strain order is defined by the octahedral tilt. At the twin walls the octahedral tilt goes to zero allowing Ti off-centering and the twin wall acquires a ferroelectric polarization [2, 3].
We have studied the intersections between different twin walls and the (001) surface using low energy electron microscopy (LEEM) and molecular dynamics simulations including Landau springs and Coulomb interactions. The domain surfaces develop polarity close to the twin walls. The elastically induced dipoles cause contrast in LEEM, unexpected for nominally non-polar surfaces. The outward and inward twin wall polarity is in good agreement with simulations.

[1] G. Catalan, J. Seidel, R. Ramesh, and J. F. Scott, Rev. Mod. Phys. 84, 119 (2012)
[2] L. Goncalves-Ferreira et al., Phys. Rev. Lett. 101, 097602 (2008)
[3] G.F. Nataf et al., Phys. Rev. Mater. 1, 074410 (2017)