Strain-induced gyrotropic effects in ferroelectric BaTiS3

Abstract: 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.