Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

摘要

The complex interdigitated phases have greatly frustrated attempts todocument the basic features of the superconductivity in the alkali metalintercalated iron chalcogenides. Here, using elastic neutron scattering,energy-dispersive x-ray spectroscopy, and resistivity measurements, weelucidate the relations of these phases inRb$_{1-\delta}$Fe$_y$Se$_{2-z}$S$_z$. We find: i) the iron content is crucialin stabilizing the stripe antiferromagnetic (AF) phase with rhombic ironvacancy order ($y\approx1.5$), the block AF phase with $\sqrt{5}\times\sqrt{5}$ iron vacancy order ($y\approx1.6$), and the iron vacancy-free phase($y\approx2$); ii) the superconducting phase ($z=0$) evolves into a metallicphase ($z>1.5$) with sulfur substitution due to the progressive decrease of theelectronic correlation strength. Both the stripe AF phase and the block AFphase are Mott insulators. Our data suggest that there are miscibility gapsbetween these three phases. The existence of the miscibility gaps in the ironcontent is the key to understanding the relationship between these complicatedphases.