Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds

Abstract

The pressure effects on the antiferromagentic orders in iron-based ladder compounds ${\text{CsFe}}_{2}{\mathrm{Se}}_{3}$ and ${\text{BaFe}}_{2}{\mathrm{S}}_{3}$ have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In ${\text{CsFe}}_{2}{\mathrm{Se}}_{3}$ the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in ${\text{BaFe}}_{2}{\mathrm{S}}_{3}$ undergoes a quantum phase transition where an abrupt increase of N\'eel temperature by more than 50% occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, ${\text{BaFe}}_{2}{\mathrm{S}}_{3}$ enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures.