Room temperature polar structure and multiferroicity in BaFe2Se3

Abstract

The understanding of the superconducting phase under pressure in the famous iron-based spin ladder ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ commands a perfect understanding of the structural properties. We present an accurate single crystal x-ray analysis which demonstrates that the structure admitted until now at room temperature is totally ruled out. We show that the system has a polar structure already at 300 K and is thus ferroelectric. Its structure is modified below the N\'eel transition and the polarization is intensified. These features unambiguously prove the multiferroic character of ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ as proposed theoretically. This system evidences a competition between multiferroicity and superconductivity.