Topological properties of the high-pressure hydride superconductor bismuth dihydride BiH 2

Topological properties and topological superconductivity in real materials have attracted intensive experimental and theoretical attentions recently. The topological electronic properties of pressure-induced superconductors BiH₂ have been studied based on first-principles electronic structure calculations. Recent experiments have revealed that BiH₂ exhibits five distinct phases under high pressure, our studies show that Cmcm-BiH₂, Pnma-BiH₂, Pnnm-BiH₂, and P2₁/m-BiH₂ are all topological metals defined on curved Fermi levels, while the P2₁2₁2₁-BiH₂ holds Weyl points near the Fermi level. The topological surface states (TSSs) and Fermi arcs of BiH₂ right cross the Fermi level and hold helical spin textures. Considering the fact that the BiH₂ exhibit high superconducting transition temperatures (Tc) of ~70 K under pressure confirmed by recent experiments, the superconducting bulks will induce superconductivity in the TSSs via the proximity effect. Thus, the hydride superconductors BiH₂ may provide a promising platform for exploring topological superconductivity and Majorana zero modes.