Superconductivity of Solid Hydrogen under Extreme Pressure

Hydrogen has the simplest crystal structure and physical properties at ambient pressure. As the pressure increases, hydrogen undergoes phase transition from insulator to metal, which being called metallic hydrogen. The numerical calculations also indicate that metallic hydrogen has high-temperature super-conductivity, thus the metal hydrogen is also known as the holy grail of physics subject. In this paper, the structural phase transition and superconducting transition temperature (T_c) of solid hydrogen under extreme high pressure 0.5–5.0 TPa were studied by first principles based on density functional theory, which may provide knowledge reserved for subsequent theoretical and experimental studies of metallic hydrogen and its superconductivity. The results show that the phase transition sequence of solid hydrogen under extreme high pressure is: I4₁/amd→oC12→cI16. For the same structure, with the increase of pressure, the electron-phonon-induced interaction decreases, the density of electronic states at the Fermi surface decreases, the vibration frequency increases, and the superconducting transition temperature changes. When the pressure is 2.0 TPa, the oC12 structure of solid hydrogen can obtain the highest T_c of 418 K (coulomb pseudopotential parameter μ^*=0.10). This work provides a reference for further theoretical and experimental research on metallic hydrogen and its superconductivity.