Self-hole-doping–induced superconductivity in KCa₂Fe₄As₄F₂

The electronic structure, magnetism, Fermi surface nesting, and bare susceptibility of the superconductor KCa₂Fe₄As₄F₂ are discussed in relation to the Fe-pnictide superconductors based on the first-principle calculations. There are ten bands crossing the Fermi level in the nonmagnetic (NM) states, resulting in six hole-like Fermi surface (FS) sheets along the $\Gamma \text{-}Z$ line and four electron-like FS sheets along the $X\text{-}P$ line. It is more complicated than other FeAs-based superconductors, showing multi-bands character. Fixed spin moment calculations and the total energies of different magnetic phase indicate that KCa₂Fe₄As₄F₂ has a strong tendency towards magnetism, i.e., the stripe antiferromagnetic state. But the self-hole-doping suppressed the spin-density wave state, and then induced superconductivity in the parent compound. Such self-doping strategy may be used for future exploration of new superconductors. (letter)