Coexistence of superconductivity and magnetic order in BaFe$_2$S$_3$: evidence for orbital-selective delocalization

Abstract

Understanding how superconductivity emerges from correlated electronic states is a central challenge in condensed matter physics. The quasi-one-dimensional spin-ladder compound \bfs\ serves as a unique platform to study this interplay, as it lacks the two-dimensional square lattice characteristic of most iron-based superconductors. Here, we combine high-pressure x-ray and neutron diffraction, x-ray emission spectroscopy, and electrical transport to map its structural, magnetic, and electronic evolution into the superconducting regime. We \revised{observe} a striking pressure-induced decoupling: while the long-range stripe-type antiferromagnetic order remains remarkably robust under pressure up to the onset of superconductivity, the local iron magnetic moment is suppressed by nearly 80\%. This dichotomy \revised{points to an orbital-selective mechanism}, where specific Fe $3d$ electrons remain localized to sustain magnetism while others delocalize to form the itinerant and superconducting state. \revised{Superconductivity emerges while long-range magnetic order is still present, revealing that the two coexist in \bfs, which we attribute to} the selective response of multiorbital electronic degrees of freedom.