Superconductivity in Li8Hn electrides: The effect of interstitial anionic electrons on electron-phonon coupling

The discovery of superconductivity in electrides, where partial electrons are localized in lattice interstices, labeled as interstitial anionic electrons (IAEs), introduces a different category known as electride superconductors. Understanding the role of IAEs in electron-phonon coupling (EPC) is crucial for the development of electride superconductors. In this study, we demonstrate that an increased net charge of IAEs enhances EPC in 12 Li8Hn (n = 4-7) electrides, exhibiting cubic/tetragonal symmetry and diverse IAEs topologies. First-principles calculations reveal a nearly linear rise in the EPC constant with the net charge of IAEs. This increase stems from the excitation effect of IAEs on Li 2p electrons and their collaborative involvement in the formation of Cooper pairs, facilitated by Li-derived low/medium-frequency phonons. This mechanism is prominently illustrated in Pm-3m Li8H4, featuring a Tc of 40.3 K, where Li atoms exhibit compressing and stretching vibrations, inducing IAEs dimerization and the strongest local EPC interaction. Conversely, hydrogen atoms in Li8Hn electrides primarily regulate the net charge and topology of IAEs. Our findings bear significant implications for the advancement of electride superconductors.