Strain-induced gyrotropic effects in ferroelectric BaTiS3

Gyrotropic effects, including natural optical activity (NOA) and the nonlinear anomalous Hall effect (NAHE), are crucial for advancing optical and transport devices. We explore these effects in the BaTiS3 system, a quasi-one-dimensional crystal that exhibits giant optical anisotropy. (Niu et al. Nat. Photonics 12, 392 (2018); Zhao et al. Chem. Mater. 34, 5680 (2022)). In the P63cm phase which is stable under room temperature, we predict two distinct strain-induced phase transitions: a symmetry-lowering transition from the P63cm to P63 phase under tensile strain, which enhances NOA and enables optical rotation; and an isostructural insulator-to-polar Weyl semimetal (WSM) transition under compressive strain, which activates the NAHE and exhibits a strain-induced sign reversal. The low-temperature P21 phase also transforms into a P212121 phase under enough compressive strains with such phase transition exhibiting a large NOA. All these results highlight BaTiS3 as a viable candidate for novel ferroelectrics, optical and transport devices with strain enhanced or activated gyrotropic properties.