Topological and superconducting states in monolayer CrH₂

The interplay of superconducting and topological states in two-dimensional (2D) materials has gained intensive attention for exploring novel quantum phenomena and their applications in quantum computing. However, 2D materials exhibiting both superconductivity and topological phases are exceptionally rare. In this context, we investigated 2D CrH₂(chromium dihydride) in P-6m2 (hexagonal) and P-3m1 (trigonal) symmetries using first-principles calculations. We verified the stability of these phases using phonon dispersion and mechanical stability analyses. Based on our<i>Z</i>₂invariant calculations, CrH₂is topologically nontrivial for the P-6m2 symmetry, while it is topologically trivial for the P-3m1 symmetry. Using anisotropic Migdal-Eliashberg equations, we find both phases as single-gap superconductors, with transition temperatures of ∼11 K for the hexagonal phase and ∼8 K for the trigonal phase. The superconducting properties are attributed to electron-phonon coupling between Cr-<i>d</i>orbitals and low-energy phonon modes dominated by Cr vibrations. Our findings offer a promising foundation for further exploration of co-existence of topological and superconducting states in monolayer hydrides and their experimental realization.