Asymmetric Spin Canting and Demagnetization Dynamics Driven by Laser Fields in Two-Dimensional Altermagnets

Laser-induced ultrafast magnetization dynamics have been well established in conventional magnets but remain unexplored in altermagnets (AMs). Using real-time time-dependent density functional theory (rt-TDDFT), we demonstrate that laser pulses can drive asymmetric demagnetization dynamics between the two Fe sublattices in the two-dimensional (2D) semiconducting AM, Fe₂WTe₄, leading to a photoinduced ferrimagnetic state with a net magnetization of approximately 0.3 μ_B per unit cell. This metastable magnetization originates from the momentum-dependent spin-splitting characteristic of d-wave AMs, which gives rise to an anisotropic optical intersite spin transfer effect (OISTR). Furthermore, the asymmetric demagnetization is accompanied by non-collinear spin dynamics, resulting in distinct spin canting angles for two Fe sublattices. Importantly, these spin dynamics are tunable by the in-plane polarization angle of the laser field. Our findings provide microscopic insight into the ultrafast control of magnetization in 2D AMs and open new avenues for light-driven manipulation of spin textures in AM systems.