Event

Seeking to understand the nature of high-temperature superconductivity (HTSC) in iron-based materials, we discuss a new class of compounds in which unconventional superconductivity may occur.  When first discovered in 2008, superconductivity in iron-containing materials was thought to manifest by charge doping materials with metallic normal states.  By 2011, superconductivity was found, surprisingly, to also emerge from systems showing insulating and pseudo-gapped normal states. Studying the novel insulators La2O2Fe2OM2 (M=S, Se), called iron oxychalcogenides (FeOCh), we found that different electron correlation features can be enhanced or diminished as observed in X-ray spectroscopic data. We report the presence of exotic electronic properties: the new insulators possess sizable local Coulomb correlation and inter-orbtial hybridization similar to Mott and Kondo insulators. These materials have been named Mott-Kondo Insulators. We have shown that their non-magnetically ordered state could be made more metallic by exchanging sulfur with selenium indicating that further metallic enhancement might be achieved through carrier doping or external pressure. We predict that the Mott-Kondo Insulators should be tunable into the unconventional superconducting state.