Possibility of Skyrmion Superconductivity in Doped Antiferromagnet K$_2$Fe$_4$Se$_5$

Abstract

Intercalated Fe chalcogenide K$_2$Fe$_4$Se$_5$ family exhibits high Tc ($\sim$ 30 K) superconductivity and spin-8 high T$_{\rm N}$ ($\sim$ 560 K) antiferromagnetism (AFM). We present a model Hamiltonian and suggest \textit{Skyrmion superconductivity}. A doped electron creates an orbitally non degenerate S=7\half state in a F$_4$Se$_9$ cluster and moves in a single correlated band, exchange coupled to a robust S=8 AFM order. Skyrmion, a topological excitation of 2 dimensional AFM order acquires an \textit{induced charge -2e} through a quantum anomaly and becomes a Cooper pair. Superconductivity emerges for a range of doping. Fluctuating superconductivity, arising from preformed Cooper pairs (stable Skyrmions), around room temperatures is predicted. We offer hope for higher Tc's in large-S Mott insulators.