Charge disproportionation, mixed valence, and Janus effect in multiorbital systems: A tale of two insulators


Phys. Rev. Lett. 122, 186401


May, 2019


Aldo Isidori, Maja Berovic, Laura Fanfarillo, Luca de' Medici, Michele Fabrizio, Massimo Capone

Multiorbital Hubbard models host strongly correlated 'Hund's metals' even for interactions much stronger than the bandwidth. We characterize this interaction-resilient metal as a mixed-valence state. In particular it can be pictured as a bridge between two strongly correlated insulators: a high-spin Mott insulator and a charge-disproportionated insulator which is stabilized by a very large Hund's coupling. This picture is confirmed comparing models with negative and positive Hund's coupling for different fillings. Our results provide a characterization of the Hund's metal state and connect its presence with charge disproportionation, which has indeed been observed in chromates and proposed to play a role in iron-based superconductors.