Strong enhancement of superconductivity in inorganic electride 12CaO·7Al₂O₃:e^- under high pressure

We present the results of the pressure dependence of the superconductivity of the inorganic electride 12CaO·7Al₂O₃:e^- (C12A7:e^-) single crystal through the ac-susceptibility measurement under high pressure. C12A7:e^- has the cage structure and the density of states derived from the cages may play an important role in the superconductivity. The superconducting transition temperature (T _c) is ∼ 0.2 K at ambient pressure and monotonically increases up to 1.79 K at 4.7 GPa. The upper critical field H _c2 and -dH _c2/dT at T _c, in proportion to the density of states (DOS) at Fermi energy becomes larger under high pressure. The superconductivity in C12A7:e^- is mediated by the electron-phonon interaction, and the increase of Tc with pressure may arise from a peak structure of the DOS of cage conduction band.