Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

BaFe2Se3 a quasi-unidimensional non-centrosymmetric superconductor

S. Deng, A. Roll, W. G. Zheng, T. Vasina, D. Bounoua, P. Fertey, M. Verseils, C. Bellin, A. Forget, D. Colson, M. B. Lepetit, P. Foury-Leylekian, V. Balédent

Abstract

The spin-ladder compounds of the BaFe2X3 (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 \bfse\ 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 \bfse\ 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.

BaFe2Se3 a quasi-unidimensional non-centrosymmetric superconductor

Abstract

The spin-ladder compounds of the BaFe2X3 (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 \bfse\ 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 \bfse\ 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.
Paper Structure (6 sections, 4 figures, 1 table)

This paper contains 6 sections, 4 figures, 1 table.

Table of Contents

  1. Experimental methods.
  2. X-ray diffraction.
  3. Lattice dynamics.
  4. Ab-initio calculations.
  5. Conclusion.
  6. Aknowledgment.

Figures (4)

  • Figure 1: (Color online) Reconstructions of the reciprocal space at 12 GPa (a) at low temperature in the (H,0,L) plane perpendicular to the ladders in the monoclinic setting and (b) at ambiant temperature in the (H,K,0) plane perpendicular to the ladders in the $Cmcm$ setting. Insets show the lattice unit in red with the direct lattice vectors in their respective settings.
  • Figure 2: (Color online) a and c : Reflectivity of BaFe$_2$Se$_3$ as a function of energy and pressure for $\mathbf{E} \parallel \mathbf{c}$ ($B_{1u}$) and $\mathbf{E} \parallel \mathbf{a}$ ($B_{3u}$) in $Cmcm$ setting, respectively. The value of the reflectivity at 310 $\rm cm^{-1}$ has been subtracted to remove the baseline shift due to progressive metallization. Panels b and d show selected reflectivity at 2 GPa (blue line) and 5 GPa (red line) for both polarizations. The fit of the reflectivity is represented by the black line, and the difference between the data and the fit is shown in the corresponding color. Arrows indicate the positions of the fitted phonons.
  • Figure 3: (Color online) Raman spectra of BaFe$_2$Se$_3$ at 1.6 (blue line) and 4.8 GPa (red line) at 300K for both polarizations of the incident light (left : $\mathbf{E} \parallel \mathbf{c}$ corresponding to Z(YY)Z; right $\mathbf{E} \parallel \mathbf{a}$ corresponding to X(YY)X with X,Y,Z along a,b,c in $Cmcm$ setting). They belong to $A_{g}$ irreducible representation in this configuration. The black line correspond to the fit with Gaussian functions.
  • Figure 4: Energy difference along the soft $P2_1/m$ to $P2_1$ phonons mode. The black curve uses the $P2_1/m$ density as starting point for the self-consistent process, while the blue one uses the density of the minimum energy point of the black curve.