Optical anisotropy in van der Waals heterostructures integrated with a low symmetry layered compound Nb₄P₂S₂₁

Two-dimensional (2D) van der Waals (vdW) materials with low crystal symmetry exhibit unique anisotropic optical and electronic properties. Here, we systematically investigate the optical modulation effects induced by anisotropic 2D materials on their isotropic counterparts in vertically stacked heterostructures. Through angle-resolved polarized Raman and photoluminescence (PL) spectroscopy of MoS₂/Nb₄P₂S₂₁ heterostructures, we observe periodic modulation of Raman and PL intensities in the intrinsically isotropic monolayer MoS₂, directly correlated with the crystallographic orientation of the anisotropic Nb₄P₂S₂₁ substrate. This phenomenon arises from strong in-plane birefringence and dichroism in Nb₄P₂S₂₁, which create a polarization-dependent Fabry-Pérot cavity that dynamically tailors the optical environment of MoS₂via cavity-mediated interference. Furthermore, we demonstrate magnetic field control of this anisotropic response through magneto-optic coupling, while polarization-resolved photocurrent measurements reveal the effect of in-plane anisotropy in Nb₄P₂S₂₁ on carrier transport in MoS₂. Our work establishes a cavity-mediated methodology to engineer light-matter interactions in isotropic 2D materials through anisotropic heterostructure design, opening avenues for developing advanced polarization-sensitive optoelectronics such as angle-resolved photodetectors and reconfigurable optical modulators.