Proposed Superconducting Electride Li6C by sp-Hybridized Cage States at Moderate Pressures

The combination of electride state and superconductivity within the same compound, e.g., [Ca24Al28O6](4+)(4e(-)), opens up a new category of conventional superconductors. However, neither the underlying causations to explain superconducting behaviors nor effects of interstitial quasiatoms (ISQs) on superconductivity remain unclear. Here we have designed an efficient and resource-saving method to identify superconducting electrides only by chemical compositions and bonding characteristics. A representative superconducting electride Li6C with a noteworthy T-c of 10 K below 1 Mbar among the known binary electrides has been revealed. Our first-principles studies unveil that the anomalous sp-hybridized cage-state ISQs, as a guest in Li6C, exhibit unexpected ionic and covalent bonds, which act as a chemical precompression to lower dynamically stable pressure. More importantly, we uncover that, contrary to common expectations, the high T-c is attributed to the strong electron-phonon coupling derived from the synergy of interatomic coupling effect, phonon softening caused by Fermi surface nesting, and phonon-coupled bands, which are mainly dominated by host sp-hybridized electrons, rather than the ISQs. Our present results elucidate a new superconducting mechanism of electrides and shed light on the way for seeking a high-T-c superconductor at lower pressures in cage-state electrides.

Automated summary

The study combines electride state and superconductivity, revealing a new category of conventional superconductors. A method is designed to identify superconducting electrides based on chemical compositions and bonding characteristics. The high T-c value is attributed to strong electron-phonon coupling effects in the electride compound, contrary to common expectations.