Pressure Induced Altermagnetism in Layered Ternary Iron-Selenides

Abstract

Employing first-principles based calculations, we reexamined the high-pressure phases of the vacancy-ordered iron-selenides, i.e. A2Fe4Se5 phase. A magnetic transition from the block-spin antiferromagnetic phase to Neel-AM phase is observed under high pressure when the iron-vacancy order is preserved. The transition is first-order, driven by the collapse of c-axis and accompanied by an insulator-metal transition. In addition, the Neel-AM phase is a rare example of intrinsic altermagnetism that does not require ligand atoms nor supercell construction to break the spatial inversion or translational symmetry between the two spin sublattices, with a spin-splitting of the band structure as large as 300 meV. If the re-entrant superconducting phase of KyFe2-xSe2 under high pressure emerges from the Neel-AM normal state, an equal-spin triplet pairing would be naturally favored.