Flat band ferromagnetism in Pb $$_2$$ 2 Sb $$_2$$ 2 O $$_7$$ 7 via a self-doped mechanism

Abstract

Abstract Electron systems with strong geometrical frustrations have flat bands, and their unusual band dispersions are expected to induce a wide variety of physical properties. However, for the emergence of such properties, the Fermi level must be pinned within the flat band. In this study, we performed first-principles calculations on pyrochlore oxide Pb $$_2$$ 2 Sb $$_2$$ 2 O $$_7$$ 7 and theoretically clarified that the self-doping mechanism induces pinning of the Fermi level in the flat band in this system. Therefore, a very high density of states is realized at the Fermi level, and the ferromagnetic state transforms into the ground state via a flat band mechanism, although the system does not contain any magnetic elements. This compound has the potential to serve as a new platform for projecting the properties of flat band systems in the real world.