Uncovering chiral phonon domains in 2D ferroelastic layered WO₂I₂

2D van der Waals (vdW) layered ferroelastic perovskites WO₂I₂ provides the unique platform understanding the underlying correlation between the spontaneous distortions of the octahedra and the intrinsic noncollinear electric dipole textures. In addition, the ferroelastic domains, depending on the anisotropic strain orientations, exhibit striped optical contrast that coincides with the linear polarization of the incident light. Here, high-quality WO₂I₂ crystals are synthesized and the angle-dependent Raman (AR) spectroscopy was conducted to verify the polarity angle between two domains by comparing AR plots on A_g1(115 cm^-1) and A_g2(753 cm^-1) modes assigned by first-principle calculations. Counterintuitively, we uncovered domain-dependent chiral phonon responses of A_g1and A_g2 modes by helicity-resolved (HR)Raman microscopy, and homogenous HR response across both domains on B_g1 mode. Revealing unbalanced 4-lobed shape symmetry, B_g1(153 cm^-1) mode in two domains are analyzed with Raman tensor calculations to interpret HR results. This realization leads to potential 2D chiral phononic applications based on 2D vdW WO₂I₂ flakes.