Stable structures and superconductivity of an At–H system at high pressure

Abstract

The phase diagram, electronic properties and superconductivity of an At–H system at high pressure are investigated through first principles calculation considering the effect of spin–orbit coupling (SOC). The Cmcm-AtH₂, Pnma-AtH₂, P6/mmm-AtH₄, and Cmmm-AtH₄ phases are uncovered above 50 GPa. Metallization is realized at 50 GPa for AtH₂ and 60 GPa for AtH₄, with T_c values of approximately 5–10 K and 30–50 K, respectively. In P6/mmm-AtH₄, phonon softening induced by Fermi surface nesting occurs as the pressure increases, which is closely related to the structural phase transition of P6/mmm → Cmmm and plays a crucial role in the superconductivity of the P6/mmm phase. In addition, the spin–orbit coupling effect considerably influences the energy of ground states, pressure points of phase transitions, electronic structures, and even the electron–phonon coupling of the At–H system. Such an influence may also occur in other heavy atomic hydrides.