Kagome Electride Superconductors Under Extreme Conditions

We investigate pressure-induced superconductivity in the electride compound Li5C and in elemental ω-Hf using density functional theory (DFT) combined with Migdal–Eliashberg theory. Despite their distinct chemistry, both systems become superconducting under compression and share a key ingredient: an electride state in which interstitial anionic electrons organize into a two-dimensional kagome topology embedded in the ionic lattice. Li5C has been proposed as a kagome-electride superconductor in the pressure range 50–210 GPa, reaching a maximum transition temperature of Tc = 48.3 K at 210 GPa, whereas pure Hf develops electride character in the 40–60 GPa regime of the high-pressure ω phase. Motivated by these developments, we first revisit Li5C and emphasize the importance of the electride state for its superconducting response. We then identify analogous kagome-electride features in ω-Hf and analyze their role in the superconductivity of compressed Hf. For ω-Hf, we show that spin–orbit coupling (SOC), which is significant in this d-band transition metal, acts in concert with electride-derived states near the Fermi level to enhance the electron–phonon coupling. This interplay provides a consistent microscopic picture of the superconducting phase and yields transition temperatures in very good agreement with previously reported experimental data.