Topological Z2 Invariants in the Metallic Bismuthide Series A 1– x T ₂ Bi ₂ ( A = Na, K, Rb, Cs; T = Zr, Hf; x = 0–0.27)

= 3 invariants for all eight compounds. This robust topological nature remains unaffected by the substitution of alkali metal and transition metal components, demonstrating that nontrivial topology is an intrinsic property of this structure type, driven by the strong spin-orbit coupling of the bismuth sublattice.