Enhanced superconductivity in CuH2 monolayers

Achieving superconductivity in hydrides at lower pressures is a long-standing scientific challenge. Here, we propose that reducing their effective dimensionality might be a possible route to achieve this goal. First-principles structural search calculations identify several two-dimensional transition metal hydrides (TMHs) with phonon-mediated superconductivity. Among them, the two CuH2 phases with P−3m1 and P−6m2 symmetries are predicted to have the highest Tc values up to 44.4 and 47.8 K, comparable to the well-known MgB2 superconductor. Their superconductivity mainly originates from the coupling of Cu3dxz/dyz and H−1s electrons with in-plane H-vibrational phonons. Interestingly, both CuH2 structures show a unique superconducting energy gap by solving the anisotropic Eliashberg equations. Furthermore, the superconductivity of TMHs is closely related to the polarity of the TM-H bond. Our paper paves the way for finding hydride superconductors in low-dimensional materials.