Metallic silicon subhydrides at high pressures studied by ab initio calculations

Kazutaka Abe

Phys. Rev. B 103, 134118 – Published 28 April 2021

Abstract

High pressure properties of silicon subhydrides SiH, ${SiH}_{2}$ , and ${SiH}_{3}$ are investigated and compared with those of ${SiH}_{4}$ by using ab initio methods. Although the subhydrides are thermodynamically unstable at lower pressures, SiH, ${SiH}_{2}$ , and ${SiH}_{3}$ are found to be stabilized above 486, 386, and 430 GPa, respectively. The predicted phases of SiH, ${SiH}_{2}$ , and ${SiH}_{3}$ have $F m \bar{3} m, I 4 / m m m$ , and $I 4 / m$ symmetries, respectively, and are metallic. The density of states suggests that the electronic states at the Fermi energy are more delocalized in the subhydrides than in ${SiH}_{4}$ . This fact is well reflected in the superconducting transition temperature ( $T_{c}$ ) estimated for ${SiH}_{2}$ and ${SiH}_{3}$ . Indeed, $T_{c}$ reaches 83 K in ${SiH}_{2}$ at 400 GPa and 88 K in ${SiH}_{3}$ at 450 GPa while that is 28 K in ${SiH}_{4}$ at 400 GPa. Although $T_{c}$ of ${SiH}_{4}$ is expected to exceed 100 K above 503 GPa, the current capability of diamond anvil cells suggests that high- $T_{c}$ silicon hydride is more likely to be attained experimentally in subhydrides.