Strain-driven stabilization of a room-temperature chiral multiferroic with coupled ferroaxial and ferroelectric order

TL;DR

This paper reports the discovery of a strain-stabilized, room-temperature chiral multiferroic phase in BaTiS$_3$, characterized by coupled ferroaxial and ferroelectric orders, enabling potential electric-field control of chirality-related phenomena.

Contribution

It introduces a novel room-temperature chiral multiferroic phase in BaTiS$_3$ stabilized by strain, with direct atomic-scale characterization and theoretical modeling of its coupled ferroaxial and ferroelectric properties.

Findings

Strain exceeding 1.5% stabilizes the chiral multiferroic phase.

Atomic resolution imaging confirms coupled ferroaxial and ferroelectric distortions.

Strong coupling predicts electric-field control of chirality-related effects.

Abstract

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 ordered 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. We report the discovery of a strain-stabilized, room-temperature chiral multiferroic phase in single crystals of BaTiS$_3$, a quasi-one-dimensional (1D) hexagonal chalcogenide. Using first-principles calculations, we predict the stabilization of this multiferroic phase having $P6_3$ space group for biaxial tensile strains exceeding 1.5% applied on the basal ab-plane of the room temperature $P6_3cm$ phase of BaTiS$_3$. The chiral multiferroic phase is characterized by rotational distortions of select TiS$_6$ octahedra around the long $c$-axis and polar displacement of Ti atoms along the $c$-axis. We used an innovative approach using focused ion beam milling to make appropriately strained samples of BaTiS$_3$. The ferroaxial and ferroelectric distortions, and their domains in $P6_3$-BaTiS$_3$ were 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 $P6_3$-BaTiS$_3$ an attractive test bed for achieving electric-field control of chirality-related phenomena such as circular photo-galvanic current and the Rashba effect.