Superconductivity in room-temperature stable electride and high-pressure phases of alkali metals

Abstract

S-band metals such as alkali and alkaline earth metals do not undergo a superconducting transition (SCT) at ambient pressure, but their high-pressure phases do. By contrast, room-temperature stable electride [Ca 24 Al 28 O 64 ] 4+ ⋅4e − (C12A7:e − ) in which anionic electrons in the crystallographic sub-nanometer-size cages have high s-character exhibits SCT at 0.2–0.4 K at ambient pressure. In this paper, we report that crystal and electronic structures of C12A7:e − are close to those of the high-pressure superconducting phase of alkali and alkaline earth metals and the SCT of both materials is induced when electron nature at Fermi energy ( E F ) switches from s- to sd-hybridized state.