Helium-bearing superconductor at high pressure

Abstract

Helium (He) is the most inert noble gas at ambient conditions. It was predicted to adopt a hexagonal close packed structure (P63/mmc) and remains in the insulating phase up to 32 TPa. In contrast, lithium (Li) is one of the most reactive metals at zero pressure, while its cubic high-pressure phase (Fd3¯m) is a weak metallic electride above 475 GPa. Strikingly, computations predict a stable compound of Li5He2 (R3¯m) by mixing Fd3¯m Li with P63/mmc He above 700 GPa from ab initio evolutionary searches. The presence of helium promotes the lattice transformation from Fd3¯m Li to Pm3¯m Li, and turns the three-dimensional distributed interstitial electrons into the mixture of zero- and two-dimensional anionic electrons. This significantly increases the degree of metallization at the Fermi level; consequently, the coupling of conductive anionic electrons with the Li-dominated vibrations is the key factor to the formation of superconducting electride Li5He2 with a transition temperature up to 26 K, dynamically stable to pressures down to 210 GPa.

Source-reported materials — not catalogue approval

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