Indirect Band Edge and Chain-Locked Linear Dichroism in the Quasi-1D Van der Waals Antiferromagnet AgCrP2S6

This work investigates the electronic and optical properties of the quasi-one-dimensional van der Waals antiferromagnet AgCrP2S6. Using polarization-resolved photoluminescence, absorption spectroscopy, resonant Raman scattering, and photoemission techniques (UPS and ARPES), the hierarchy of band-edge transitions in this material is established. The study reveals that AgCrP2S6 possesses an indirect fundamental band gap around 1.35 eV, while the lowest optically allowed direct transitions occur at higher energies (≈1.6–1.8 eV) and exhibit strong polarization dependence along the crystallographic chain axis. Resonant Raman excitation profiles and angle-resolved photoemission measurements support this interpretation of the band structure. Integration of AgCrP2S6 with graphene in a van der Waals heterostructure enables polarization-sensitive photocurrent detection, demonstrating strong linear dichroism and anisotropic optoelectronic response. These findings establish AgCrP2S6 as a promising platform for studying anisotropic excitonic physics and for developing polarization-sensitive optoelectronic devices based on low-symmetry van der Waals semiconductors.