Experimental Observation of Altermagnetism in Twisted CrPS₄ van der Waals Homostructures

Altermagnetism, characterized by compensated antiparallel spin order with finite spin splitting, bridges the properties of ferromagnets and antiferromagnets and holds great promise for next-generation spintronic applications. Theoretical studies suggest that twisting van der Waals (vdW) layers can generate altermagnetic states by engineering the interlayer symmetry, thereby expanding the family of magnetic quantum materials. However, direct experimental observation of altermagnetism in these vdW systems remains elusive. Here, we present experimental evidence to demonstrate the realization of altermagnetism in orthogonally twisted CrPS4/CrPS4 (90°- CrPS4/CrPS4) homostructures using magneto-optical spectroscopy. The symmetry of 90°-CrPS4/CrPS4 exhibits a ferromagnetic-like magnetic-field-dependent degree of circular polarization (DOCP), showing opposite variations under σ⁺ and σ⁻ excitations as the field sweeps from –9 T to 9 T. Moreover, a pronounced Zeeman splitting of ~2 meV—absent in either ferromagnetic or antiferromagnetic CrPS4—emerges in the twisted configuration, indicating a unique magnetic ground state. First-principles calculations reveal large spin-split bands in an antiferromagnetic configuration, confirming the realization of altermagnetism in 90°- CrPS4/ CrPS4. Polarized Raman spectroscopy further identifies interlayer-coupling-induced phonon mode splitting unique to the altermagnetic state. These findings provide the first experimental observation of altermagnetism in a twisted vdW material and establish a versatile platform for engineering symmetry-driven spin-split states, opening new avenues for spintronic and quantum information technologies.