Mott-Kondo insulator behavior in the iron oxychalcogenides

We perform a combined experimental-theoretical study of the Fe-oxychalcogenides (FeO Ch) series La2O2Fe2OM2 (M = S, Se), which are among the latest Fe-based materials with the potential to show unconventional high-T-c superconductivity (HTSC). A combination of incoherent Hubbard features in x-ray absorption and resonant inelastic x-ray scattering spectra, as well as resistivity data, reveal that the parent FeO Ch are correlation-driven insulators. To uncover microscopics underlying these findings, we perform local density approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that reveal a novel Mott-Kondo insulating state. Based upon good agreement between theory and a range of data, we propose that FeO Ch may constitute an ideal testing ground to explore HTSC arising from a strange metal proximate to a novel selective-Mott quantum criticality.