A new aspect of the charged domain wall in hexagonal RMnO₃ systems (R: Y, In)

We investigate the profiles of the polarization in the simple “flat” charged domain wall, specified by “head to head” (“tail to tail”) configuration, in the hexagonal RMnO₃ systems (R: Y and In). Detailed observations of profiles of the displacements of Y-ions (In-ions) across the above-specified domain walls have been carried out utilizing the HAADF-STEM method with the resolution as high as 20 picometers. The results show qualitatively different features from the conventionally accepted tanh(x) type polarization profile in the domain wall. Taking into account that the non-polar state exists as a (meta)stable one in addition to the two degenerate polar states, the analysis of the obtained experimental results has been carried out based on one-dimensional ϕ⁶ field theory. The theoretical results have shown satisfactory consistencies with experimental observations. We also recognize that the present problem may be discussed in the framework of “interacting (either attractive or repulsive) soliton pair”. In this context, YMnO₃ corresponds to the case where the attractive interaction dominates, resulting in merging of the solitons while InMnO₃ to the case where the repulsive interaction dominates, resulting in the completely separated configuration of the two solitons. These pictures provide a new perspective to understand the “charged” domain wall in the materials under consideration.