Temperature Dependent THz Spectroscopy of the Quasi-1D van der Waals Semiconductor AgCrP₂S₆

AgCrP₂S₆ (ACPS) is a layered van der Waals semiconductor whose Cr sublattice forms quasi-1D zigzag spin chains. In recent years, this material has attracted wide attention for low-dimensional long-range magnetic ordering and strong in-plane transport anisotropy. ACPS develops anisotropic antiferromagnetic order near 21 K, and shows spin-lattice anomalies near 120 K. Aiming to study the material's strong in-plane anisotropy and possible spin–lattice coupling, we performed temperature-dependent terahertz transmission spectroscopy on bulk ACPS over a wide frequency range (~1–18 THz). Terahertz spectroscopy provides a direct broadband, phase-sensitive window on low-energy electrodynamics, accessing phonons, magnons, hybrid excitations, and charge dynamics. We observe additional absorption features that become evident only at high temperatures and remain observable up to room temperature. These measurements provide a baseline for future work to separate spin, lattice, and symmetry effects in ACPS.