Twist-Induced Giant Modulation of Optical and Optoelectronic Anisotropy in van der Waals NbOX₂ Homo-/Heterostructures.

Abstract

Layered NbOX₂ (X = Cl, I) materials have recently attracted significant attention owing to their intrinsic in-plane ferroelectricity and anisotropic optical and electronic properties, while the nondestructive modulation of their optical and optoelectronic anisotropy responses remains challenging. In this work, we propose a nondestructive approach to modulate the optical and optoelectronic anisotropy in multilayer NbOX₂ by constructing homo/heterostructures with tunable twist angles. By constructing stacked NbOCl₂ homostructures (or NbOCl₂/NbOI₂ heterostructures) and precisely tuning the twist angle, we achieve giant modulation of both optical reflection anisotropy and Raman scattering anisotropy, ranging from pronounced anisotropy to complete isotropy. The observed modulation can be attributed to optical superposition and is well modeled by linear electromagnetic theory. Moreover, we realize polarization-programmable photodetectors using twisted NbOI₂ homostructures, where distinct anisotropic and isotropic photoresponses are simultaneously achieved within a single device. This study offers an effective strategy for tailoring optical and optoelectronic anisotropy in layered ferroelectrics.