Fe-based superconductors: Crystallochemistry, band structure and phase diagrams

The discovery of Fe-based superconductors (Fe-SC) with relatively high superconducting transition temperature (Tc) represents a fundamental result in the field of the solid state physics and a milestone in the history of superconductivity. In fact, these materials exhibit the highest Tc after Cu-SC. The former superconducting compounds belonging to this class of materials, LaFePO and LaNiPO (Kamihara et al. 2006; Watanabe et al. 2007), where synthesized since 2006, but did not attracted much interest, due to their relatively low superconducting transition temperatures (Tc = 4 K). The breakthrough occurred in February 2008, when a Tc ~ 26 K was reported for LaFeAs(O1-x F x) (Kamihara et al. 2008); this discovery definitely triggered the extensive interdisciplinary researches on Fe-SC, relaunching the research in superconductivity. A few weeks later, a Tc ~ 55 K was measured for SmFeAs(O1-x F x) compositions (Zhi-An et al. 2008), a value that still represent the highest Tc attained in the Fe-SCs. A new family of compounds was discovered after a few months, when a Tc ~ 38 was achieved by hole-doping (K-substitution) BaFe2As2 (Rotter et al.). 173After several years, Fe-SC are still the subject matter of many researches and new developments are ongoing