Pressure-driven phase transition from antiferromagnetic semiconductor to nonmagnetic metal in the two-leg ladders AFe2X3 (A=Ba,K; X=S,Se)

The recent discovery of superconductivity in BaFe₂S₃ has stimulated considerable interest in 123-type iron chalcogenides. This material is the first reported iron-based two-leg ladder superconductor, as opposed to the prevailing two-dimensional layered structures of the iron superconductor family. Once the hydrostatic pressure exceeds 11 GPa, BaFe₂S₃ changes from a semiconductor to a superconductor below 24 K. Although previous calculations correctly explained its ground-state magnetic state and electronic structure, the pressure-induced phase transition was not successfully reproduced. In this work, our first-principles calculations show that with increasing pressure the lattice constants as well as local magnetic moments are gradually suppressed, followed by a first-order magnetic transition at a critical pressure, with local magnetic moments dropping to zero suddenly. Our calculations suggest that the self-doping caused by electrons transferred from S to Fe may play a key role in this transition. The development of a nonmagnetic metallic phase at high pressure may pave the way to superconductivity. As extensions of this effort, two other 123-type iron chalcogenides, KFe₂S₃ and KFe₂Se₃, have also been investigated. KFe₂S₃ also displays a first-order transition with increasing pressure, but KFe₂Se₃ shows instead a second-order or weakly first-order transition. Here, the required pressures for KFe₂S₃ and KFe₂Se₃ to quench the magnetism are higher than for BaFe₂S₃. Further experiments could confirm the predicted first-order nature of the transition in BaFe₂S₃ and KFe₂S₃, as well as the possible metallic/superconductivity state in other 123-type iron chalcogenides under high pressure.