Twist-Induced Altermagnetism in a Metallic van der Waals Antiferromagnet

Altermagnetism offers a promising route for next-generation spintronic devices. In two-dimensional (2D) magnets, twist engineering enables its realization by breaking the combined inversion and time-reversal symmetry ($P$T). Here, by first-principles calculations and symmetry analysis, we demonstrate that twisting the recently synthesized metallic van der Waals antiferromagnet Co-doped bilayer Fe₃GaTe₂ (Fe₂CoGaTe₂) provides a robust platform for altermagnetism, breaking the $P$T symmetry between opposite spin sublattices. This results in a nonrelativistic i-wave altermagnetic state with spin splitting up to 138 meV. Without spin-orbit coupling (SOC) the electronic states remain spin-degenerate along six high-symmetry directions, whereas including SOC preserves degeneracy along the three directions protected by 2-fold rotation axes. Furthermore, we unveil the microscopic mechanisms governing the magnetic behavior in twisted bilayer Fe₂CoGaTe₂. Our results establish twist engineering and metallic Fe-based van der Waals antiferromagnets as versatile platforms to realize 2D altermagnetism, with potential for designing high-efficiency ultrathin nanodevices.