Abstract
The recent discovery of superconductivity in BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] 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. 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.
