Iron-based superconductors under heavy compression after destruction of superconductivity

Choosing electron and hole doped Ba$_{1-y}$K$_{y}$Fe$_{2-x}$A$_{x}$As$_{2}$ (A=Ni,Co) and Fe$_{1+y}$Se$_{1-x}$Te$_{x}$ -- typical iron pnictides and chalcogenides, we investigate pressure effects on the physical properties of these superconductors after their superconductivity is completely destroyed. Combining electrical resistance and magnetic susceptibility measurements at pressures above 60 GPa, we establish extended pressure - temperature phase diagrams for these compounds. Contrary to the general belief of the existence of Fermi liquid after the disappearance of superconductivity upon compression, we find an unexpected insulating state in these heavily compressed compounds. Some novel behaviors such as reentrance of superconductivity are also discovered. These results indicate that rich physics is still hidden in iron-based superconductors.