Iron-Based Superconductors: A Decade of Materials, Magnetism, and Mechanisms

Abstract

Since its discovery in 2008, iron-based superconductors (FeSCs) have become a central platform for exploring high-temperature superconductivity in multiband, electron-correlated materials. This review focuses on major developments over the past decade or so, emphasizing experimental advances, pairing mechanisms, and emerging applications. Structural tuning through chemical substitution, pressure, and epitaxial growth enables precise control of the electronic, magnetic, and superconducting ground states, thereby revealing their interplay. In particular, the electronic nematic phase and stripe-type antiferromagnetic order-often coexisting or competing-are central to understanding the phase diagrams. Spin waves in magnetically ordered parent compounds and spin excitations (fluctuations) in doped superconductors are extensively characterized by inelastic neutron scattering. While high-energy spin excitations in doped superconductors retain substantial spectral weight across a wide energy range reminiscent of spin waves in their undoped parents, the low-energy response reveals a collective spin excitation termed ``resonance'' coupled to superconductivity. The momentum structure of superconductivity-induced resonance provides strong evidence for sign-changing pairing in many FeSCs, while disorder effects, orbital-fluctuation scenarios, quasiparticle damping, and compound-dependent gap structures indicate that $s_{\pm}$, $s_{++}$, nodal $s$, $d$-wave, and multicomponent states must be discussed in a material-specific framework. Advances in thin-film growth, intercalation chemistry, and interface engineering-particularly in FeSe-based systems-have enabled enhanced $T_{c}$ and novel device geometries. With high upper critical fields, moderate anisotropy, and improving current densities, FeSCs continue to drive both fundamental insight and technological applications in superconductivity.