Indirect Band Edge and Chain‐Locked Linear Dichroism in the Quasi‐1D Van der Waals Antiferromagnet AgCrP ₂ S ₆

ABSTRACT AgCrP ₂ S ₆ (ACPS) is an exciting antiferromagnetic material in which van der Waals structure combines with low crystal symmetry and a quasi‐1D Cr‐based spin‐chain network, giving rise to pronounced directional anisotropy in its optical and electronic properties. Despite its promise for exploring 1D physics, uncertainties in its band‐edge electronic structure limit its application potential. In this work, we combine polarization‐resolved optical spectroscopy, photoemission, and photocurrent measurements to establish the hierarchy of band‐edge transitions in ACPS. We find that the fundamental gap is indirect, appearing as a photoluminescence band at ≈1.35 eV without a corresponding absorption resonance. Instead, the first allowed direct transitions emerge at higher energies (≈1.63–1.76 eV) for light polarized along the chain axis. Resonant Raman excitation profiles, together with photoemission measurements, support these findings by locating Γ‐coupled electronic resonances and placing the valence‐band maximum ≈1.56 eV below E _F . Finally, integration of ACPS with graphene into a heterostructure enables polarization‐sensitive photocurrent collection that mirrors the optical selection rules with an onset ≳1.5 eV and an anisotropy ratio of ≈0.53.