Reversibly controlled ternary polar states

Anisotropic interaction between electric/magnetic dipoles often produces intriguing physical phenomena, such as exchange bias in the magnetic heterostructure and magnetoelectric coupling in multiferroics. For ferroelectrics, rather than a cooperative dipolar unit element, the spatial electric potential gradient has imitated such interactions with electric dipoles. The defect-dipole, as a dipolar unit element, tends to be considered the undesired to deteriorate the ferroelectric functionality. In this talk, we report that square-tensile-strained BaTiO₃ produces in-plane spontaneous polarization, four-variants domains, and the defect-dipole, where their cooperation yields reversible control of ternary polar states.