Electrides as a New Platform of Topological Materials

Research on the topological properties of the wave function attracts a great deal of attention [1]. In our presentation, we show that electrides are suitable for achieving various topological insulating and topological semimetal phases [2]. In electrides, some electrons reside in the interstitial regions and act as anions to stabilize the structure. Since interstitial electrons have small work function, band inversion around the Fermi level is likely to occur. We find that Sc₂C shows nontrivial insulating phase characterized by the π Zak phase. This π Zak phase appears as a surface polarization charge, and we propose that this surface charge is useful for carrier doping by using the electride. We find various topological electrides such as Y₂C, Sr₂Bi (nodal-line semimetal), HfBr (quantum spin Hall system), and LaBr (quantum anomalous Hall insulator). We also discuss one-dimensional electride materials as topological electrides with corner charges.
[1] M.Hirayama, R. Okugawa, and S. Murakami, J. Phys. Soc. Jpn. 87, 041002 (2018). (Review) [2] M.Hirayama, S. Matsuishi, H. Hosono, and S. Murakami, Phys. Rev. X 8, 031067 (2018).