Speaker
Description
The spin-ladder compounds of the BaFe$_2X_3$ ($X$ = chalcogen) family may be viewed as dimensional reductions—along stripe-like 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 BaFe$_2$Se$_3$ 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 non-centrosymmetric, adopting the polar space group $P2_1$. These findings not only revise the structural assignment of BaFe$_2$Se$_3$ in its superconducting state but also establish its non-centrosymmetric character—an essential ingredient for potential unconventional pairing mechanisms—thereby opening new perspectives on the interplay between lattice symmetry, dimensionality, and superconductivity in iron-based materials.
Reference:
[1] S. Deng, A. Roll, W.G. Zheng, G. Giri, T. Vasina, D. Bounoua, P. Fertey, M. Verseils, C. Bellin, A. Forget, D. Colson, P. Foury-Leylekian, M. B. Lepetit, and V. Baledent, Physical
Review B, 113(12), L121105 (2026)