Deterministic Switching in Altermagnets via Asymmetric Sublattice Spin Current

We demonstrate a deterministic switching mechanism in collinear altermagnets driven by asymmetric sublattice spin currents. Unlike conventional antiferromagnets, where combined parity-time-reversal symmetry enforces purely staggered sublattice spin torques, altermagnets host symmetry-protected nonrelativistic spin splitting that produces unequal torques on the two sublattices. Using doped FeSb$_2$ as a representative $d$-wave altermagnet, our Landau--Lifshitz--Gilbert simulations show that these torques enable magnetic-field-free and deterministic 180$^\circ$ N\'eel vector reversal over picosecond timescale. The mechanism is generic to even-parity altermagnets and remains effective even in centrosymmetric, weak spin-orbit coupled systems, where the N\'eel spin-orbit torque mechanism fails. Our results establish an experimentally accessible mechanism for switching of altermagnetic order, opening pathways for realizing ultrafast, low-power altermagnet spintronic devices.