Altermagnetism, Kagome Flat Band, and Weyl Fermion States in Magnetically Intercalated Transition Metal Dichalcogenides

Altermagnetic (AM) compounds have recently emerged as a promising platform for realizing unconventional quantum phases, enabled by their unique spin-split band structure at zero net magnetization. Here, we report first-principles investigation of magnetically intercalated transition metal dichalcogenides (TMDs) of general form 𝑋𝑌₄𝑍₈ (𝑋 = Mn, Fe, Co, Ni, Cr, or V; 𝑌 = Nb or Ta; and 𝑍 = Se or S), identifying new candidates for altermagnetic behavior. Our results reveal a direct correlation between the materials' interatomic geometry and the resulting magnetic ground state. Systems that exhibit A-type antiferromagnetic order display momentum-dependent spin-splitting consistent with altermagnetic behaviour. Crucially, the interplay between AM spin-splitting and spin-orbit coupling leads to the formation of Weyl nodes and topological surface states in the form of Fermi arcs. Additionally, we identify kagome-like flat bands near the Fermi level, emerging from the perturbation induced by intercalant atoms that form an effective kagome-like sublattice within the TMD layer. These findings establish magnetically intercalated TMDs as a unique and robust material family that unifies altermagnetism, flat bands, and Weyl fermions. This multifunctionality makes them highly promising for advancing next-generation topological and spintronic applications.