Most interesting physics in condensed matter is always related to the quantum mechanics of localized electrons tightly, with magnetic transition and the accompanied volume collapse, the strong correlation and high-temperature superconductivity (as well as the isostructure transition in cerium), and insulator-metal transition as some of the typically known examples. In all of these systems, the electrons are either localized to ions, or forming covalent states that binding separated atoms. In contrast, in electrides, a class of emerging materials, the electrons unconventionally localized to interstitial sites, leading to strong electron-phonon coupling and cation-ISQ polarization that is quite different from the traditional anion-cation polarization in ionic compounds, thus has the possibility to host unprecedented new physics. In this talk, I will show three novel possible physical phenomena, i.e., the colossal negative charge state of metallic element that violates the octet rule in chemistry, the LA-TA splitting in phonon spectra that beyond the standard lattice dynamics, and the universal but robust metallic surface state that beyond the standard topology band theory, that are intriguing but unique in electrides. All of these phenomena are consequence of off-atomic localization of electrons, as well as the resulted atom-ISQ polarization. These demonstrations indicate that electride might be an unexplored territory in condensed matter that host new physics, and experimental efforts to verify these theoretical predictions are called for.

electride,electronic structure,localization-delocalization transition,polarization,quantum mechanics