Realizing high-Tc ambient-pressure superconductivity in hole-doped hydride Mg(BH4)2

Hydrogen-based superconductors provide a promising route to the long-sought goal of room-temperature superconductivity (SC), however, ultrahigh pressure required to maintain their structural stability hinders the experimental investigation and potential applications. Here, we propose a novel route to design high-Tc hydride superconductors at ambient pressure by hole doping into previously reported hydrogen storage material Mg(BH4)2. Based on the first-principles calculations, we found that with a moderate hole doping of 0.1 holes per formula unit, the insulator Mg(BH4)2 transforms into the metal accompanied by the emergency of large B-H sigma electronic states at the Fermi level (EF), and thus strong electron-phonon coupling SC is obtained with Tc up to -100 K, and with further increase of hole-doped concentration, the Tc can be promoted to 140 K. Additionally, the topological analysis demonstrates that the hole-doped Mg(BH4)2 has symmetry-protected Dirac nodal lines around the EF, giving rise to the delicate surface states. These findings indicate that Mg(BH4)2 not only provides an ideal candidate to attain high-Tc SC by hole doping at ambient pressure, but also to explore more exotic physics for the coexistence of high-Tc SC and topology.