Ultrafast Laser-Driven Asymmetric Demagnetization Dynamics in <i>d</i> -Wave Altermagnets

Altermagnetism (AM), an unconventional spin-ordered phase, presents a unique platform for exploring ultrafast spin manipulation. However, the mechanisms underlying laser-driven spin dynamics in low-dimensional altermagnets remain largely unclear. Using real-time time-dependent density functional theory, we investigate laser-induced spin dynamics in <i>d</i>-wave AM V₂Se₂O-based crystals. Our results show that momentum-dependent spin transfer in them can be selectively excited by laser polarization, generating a transient net magnetization via anisotropic optical intersite spin transfer. Compared with K-intercalated bulk KV₂Se₂O, deintercalated bulk and monolayer V₂Se₂O exhibit a much larger laser-induced net magnetization, which is attributed to the K-intercalation controlled electronic reconstruction and the consequent suppression of spin-relaxation channels. These results establish dimensionality and K-intercalation as practical knobs to tailor ultrafast spin responses, highlighting altermagnets as viable candidates for ultrafast spintronic applications.