Quadruple-well ferroelectricity and topological domain structures in strained Bi2O2Se.

Exotic dipole orders and topological domain structures in ferroelectrics are intriguing both for fundamental physics and device applications. Herein, based on DFT calculations, Monte Carlo and phase-field modeling, we reveal that appropriate strain engineering can enable a ferroelectric transition in high-mobility semiconductor bismuth oxyselenide Bi₂O₂Se throughout the entire 3D space. Furthermore, we explore the ferroelectric properties of Bi₂O₂Se under different strain conditions. Uniaxial strain induces a typical double degenerate ferroelectric state, while biaxially strained Bi₂O₂Se holds unusual quadruple-well dipole orders and a "two-step" 90° ferroelectric switching. These ferroelectric phase transitions are temperature-limited. More importantly, various types of spontaneous topological domain structures in biaxially strained ferroelectric Bi₂O₂Se are demonstrated, including vortex and anti-vortex patterns. Our work is expected to enrich the understanding of ferroelectric effects in Bi₂O₂Se, which is essential for practical application of ferroelectrics in next-generation high-performance functional electronic devices. [ABSTRACT FROM AUTHOR]