Electronic properties of alkali-metal loaded zeolites: Supercrystal Mott insulators

First-principles band calculations are performed for an open-structured zeolite with guest atoms (potassium) introduced in the cages. A surprisingly simple band structure emerges which indicates that this system may be regarded as a ``supercrystal,'' where each cluster of guest atoms with diameter ~10 acts as a ``superatom'' with well-defined s- and p-like orbitals, which in turn form tight-binding bands around the Fermi energy. The calculated Coulomb energy for these states turns out to be in the strongly correlated regime. We show, with the dynamical mean-field theory, that the system resides in the Mott-insulator regime in accord with experimental results. We envisage that this class of systems can provide a new avenue for materials design.