Realization of Mott-insulating electrides in dimorphic Yb5Sb3

Electrides are exotic compounds that confine anionic electrons in periodically distributed subnanometer-sized spaces. Such trapped electrons are free from onsite electron-nuclear interaction and exhibit unconventional properties. Here, we report that \ensuremath{\alpha}- and $\ensuremath{\beta}\ensuremath{-}\mathrm{Y}{\mathrm{b}}_{5}\mathrm{S}{\mathrm{b}}_{3}$ are inorganic electrides exhibiting Mott-insulating features. Anionic electrons are stabilized in the quasi-one- and -zero-dimensional spaces, and give rise to the corresponding electride bands near their Fermi levels. Despite the partially occupied electronic picture, both of these systems exhibit semiconducting conductivity and Curie-type magnetism with $S=1/2$ moments, demonstrating electron localization. These findings show that anionic electrons can serve as magnetic centers, and inorganic electrides have the potential to act as strongly correlated materials even without the presence of localized atomic orbitals.