Sliding-Controlled Switchable In-Plane Altermagnetic Ferrovalley States and Strong Optical Response in Cr ₂ WS ₄ for Applications in Valleytronic Devices

Ferrovalleytronic materials, which harness both valley degrees of freedom and spin, provide a promising platform for cutting-edge spintronic devices. However, their realization remains largely limited to systems with out-of-plane magnetization and often requires an external stimulus. Here, using first-principles calculations, we not only identify Cr 2 WS 4 as an intrinsic in-plane altermagnetic ferrovalleytronic material but also show that spin-valley locking and valley splitting are governed mainly by crystal symmetry rather than spin–orbit coupling, marking a paradigm shift in the selection of candidate systems for ferrovalleytricity. We first show that the Cr 2 WS 4 monolayer exhibits in-plane altermagnetism characterized by large nonrelativistic spin splitting in momentum space. Next, we demonstrate that the interlayer sliding in the altermagnetic Cr 2 WS 4 bilayer can induce ferrovalley states of up to 86 meV with the valley sign intrinsically controlled by the stacking configuration. Such a large valley splitting significantly exceeds the thermal energy at room temperature, providing a robust material platform for next-generation valleytronic devices operable without cryogenic conditions. Furthermore, the light-harvesting capability of Cr 2 WS 4 is assessed for potential solar cell applications by calculating its optical absorption spectra, which reveal significantly enhanced absorption across the visible and ultraviolet regions compared to that of well-studied black phosphorene. These findings highlight Cr 2 WS 4 as a promising candidate for multifunctional valleytronic, spintronic, and optoelectronic devices and motivate further experimental investigation.