Helium-bearing superconductor at high pressure

TL;DR

This paper reports the discovery of a helium-bearing superconductor, Li5He2, formed at high pressure, which exhibits superconductivity with a transition temperature up to 26 K due to enhanced metallization and electron coupling.

Contribution

It introduces a new high-pressure helium-lithium compound that becomes superconducting, revealing novel interactions between helium and metallic electrons under extreme conditions.

Findings

Li5He2 is stable above 700 GPa and superconducts up to 26 K.

Helium promotes lattice transformation and enhances metallization.

Superconductivity persists down to 210 GPa.

Abstract

Helium (He) is the most inert noble gas at ambient conditions. It adopts 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 (Fd-3m) is a weak metallic electride above 475 GPa. Strikingly, a stable compound of Li5He2 (R-3m) was formed by mixing Fd-3m Li with P63/mmc He above 700 GPa. The presence of helium promotes the lattice transformation from Fd-3m Li to Pm-3m Li, and tuns 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.