Superconducting dense lithium-based germanides with electride states
Qianyi Wang, Jiahui Wei, Ting Zhong, Jiance Sun, Bo Gao, Li Zhu, Hanyu Liu, Shoutao Zhang
Abstract
Lithium-based electrides with interstitial anionic electrons (IAEs) have recently garnered a great deal of attention, since these materials were found to host intriguing properties such as multiple IAE arrangements and potential superconductivity. In this study, we here conducted comprehensive simulations on the pressure-induced stable Li-abundant germanides leveraging the advanced first-principles structure predictions. As a consequence, our simulations identified several metallic Li-Ge electride phases with robust stability, i.e., $\mathrm{L}{\mathrm{i}}_{5}\mathrm{Ge}, \mathrm{L}{\mathrm{i}}_{6}\mathrm{Ge}, \mathrm{L}{\mathrm{i}}_{7}\mathrm{Ge}, \mathrm{L}{\mathrm{i}}_{8}\mathrm{Ge}$, and $\mathrm{L}{\mathrm{i}}_{10}\mathrm{Ge}$. Strikingly, the evolution from connected one-dimensional (1D) to zero-dimensional (0D) electride states of $\mathrm{L}{\mathrm{i}}_{5}\mathrm{Ge}$ was identified concurrent with an orthorhombic $Cmcm$ to triclinic $C2/c$ phase transition on account of compression-induced volume reduction, whereas $\mathrm{L}{\mathrm{i}}_{10}\mathrm{Ge}$ possesses the unusual coexistent 0D and 1D IAEs. Electron-phonon coupling (EPC) calculations uncover that the superconductivity of $Cmcm \mathrm{L}{\mathrm{i}}_{5}\mathrm{Ge}$ is superior to that of $C2/c \mathrm{L}{\mathrm{i}}_{5}\mathrm{Ge}$ at 50 GPa, which is due to the larger EPC strength, higher density of states at the Fermi level, and more pronounced softened phonon modes of $Cmcm \mathrm{L}{\mathrm{i}}_{5}\mathrm{Ge}$. Remarkably, $\mathrm{L}{\mathrm{i}}_{10}\mathrm{Ge}$ was calculated to have the highest superconducting critical temperature (${T}_{c}$) of 8.5 K below 50 GPa compared to other lithium-carbon family electrides, which is ascribed to the fact that the Li $2p$ electron states near the Fermi energy are strongly coupled with phonon modes associated with the vibrations of Li atoms. Our findings provide insights into lithium-bearing electride systems with implications for the pursuit of distinguished electride superconductors.