Charged domain walls in improper ferroelectric hexagonal manganites and gallates

© 2018 American Physical Society. Ferroelectric domain walls are attracting broad attention as atomic-scale switches, diodes, and mobile wires for next-generation nanoelectronics. Charged domain walls in improper ferroelectrics are particularly interesting as they offer multifunctional properties and an inherent stability not found in proper ferroelectrics. Here we study the energetics and structure of charged walls in improper ferroelectric YMnO3,InMnO3, and YGaO3 by first-principles calculations and phenomenological modeling. Positively and negatively charged walls are asymmetric in terms of local structure and width. The wall width scales with the amplitude of the primary structural order parameter and the coupling strength to the polarization, reflecting that polarization is not the driving force for domain formation. We introduce general rules for how to engineer n- and p-type domain wall conductivity based on the domain size, polarization, and electronic band gap. This opens the possibility of fine tuning the local transport properties and designing p-n-junctions for domain wall-based nanocircuitry.