BaFe2S3: A quasiunidimensional noncentrosymmetric superconductor

Abstract

Introduction. The spin-ladder compounds of the BaFe2X3 (X = chalcogen) family may be viewed as dimensional reductions—along stripelike motifs—of the two-dimensional iron-based pnictide planes extensively studied since 2006. Remarkably, despite their reduced dimensionality, these materials retain the capacity for unconventional ground states, exemplified by the emergence of superconductivity in BaFe2Se3 under applied pressure beyond 10 GPa, following a structural phase transition at 4 GPa. Here, we report a comprehensive investigation combining high-resolution single-crystal x-ray diffraction, infrared spectroscopy, and ab initio calculations, which together elucidate the true crystallographic nature of this pressure-induced superconducting phase. While x-ray diffraction alone reveals a symmetry lowering from the widely accepted orthorhombic Cmcm group to a monoclinic structure, it lacks sufficient sensitivity to resolve the precise space group. By integrating vibrational spectroscopy with density functional theory, we provide unambiguous evidence that the high-pressure phase is noncentrosymmetric, adopting the polar space group P21. These findings not only revise the structural assignment of BaFe2Se3 in its superconducting state, but also establish its noncentrosymmetric character—an essential ingredient for potential unconventional pairing mechanisms—thereby opening different perspectives on the interplay between lattice symmetry, dimensionality, and superconductivity in iron-based materials.

Source-reported materials — not catalogue approval

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