Strain-Driven Stabilization of a Room-Temperature Chiral Multiferroic with Coupled Ferroaxial and Ferroelectric Order

Noncollinear ferroic materials are sought after as testbeds to explore the intimate connections between topology and symmetry, which result in electronic, optical, and magnetic functionalities not observed in collinear ferroic materials. For example, ferroaxial materials have rotational structural distortions that break mirror symmetry and induce chirality. When ferroaxial order is coupled with ferroelectricity arising from a broken inversion symmetry, it offers the prospect of electric-field-control of the ferroaxial distortions and opens up new tunable functionalities. However, chiral multiferroics, especially ones stable at room temperature, are rare. A strain-stabilized, room-temperature chiral multiferroic phase in single crystals of BaTiS₃ is reported here. Using first-principles calculations, the stabilization of this multiferroic phase having P6₃ space group for biaxial tensile strains exceeding 1.5% applied on the basal ab-plane of the room temperature P6₃cm phase of BaTiS₃ is predicted. The chiral multiferroic phase is characterized by rotational distortions of TiS₆ octahedra around the long c-axis and polar displacement of Ti atoms along the c-axis. The ferroaxial and ferroelectric distortions and their domains in P6₃-BaTiS₃ are directly resolved using atomic resolution scanning transmission electron microscopy. Landau-based phenomenological modeling predicts a strong coupling between the ferroelectric and the ferroaxial order making P6₃-BaTiS₃ an attractive test bed for achieving electric-field-control of chirality.