Abstract
The discovery of iron-based superconductors (FeSCs), with the highest transition temperature (Tc) up to 55 K, has attracted worldwide research efforts over the past ten years. So far, all these FeSCs structurally adopt FeSe-type layers with a square iron lattice and superconductivity can be generated by either chemical doping or external pressure. Herein, we report the observation of superconductivity in an iron-based honeycomb lattice via pressure-driven spin-crossover. Under compression, the layered FePX3 (X = S, Se) simultaneously undergo large in-plane lattice collapses, abrupt spin-crossovers, and insulator-metal transitions. Superconductivity emerges in FePSe3 along with the structural transition and vanishing of magnetic moment with a starting Tc ~ 2.5 K at 9.0 GPa and the maximum Tc ~ 5.5 K around 30 GPa. The discovery of superconductivity in iron-based honeycomb lattice provides a demonstration for the pursuit of transition-metal-based superconductors via pressure-driven spin-crossover.
Highlights
The discovery of iron-based superconductors (FeSCs), with the highest transition temperature (Tc) up to 55 K, has attracted worldwide research efforts over the past ten years
Under applied high pressure (HP), materials undergo direct structural evolutions including the shortening of metal-ligand bond length, the distortions in the nearest neighbor environment, and the introduction of stress
Applying external pressure to transition metal (TM) systems may lead to other significant phenomena such as large-volume collapse[20,21,22], spin-crossover (SCO)[22,23,24], charge disproportionation[25], and insulator-metal transition (IMT)
Summary
The discovery of iron-based superconductors (FeSCs), with the highest transition temperature (Tc) up to 55 K, has attracted worldwide research efforts over the past ten years All these FeSCs structurally adopt FeSe-type layers with a square iron lattice and superconductivity can be generated by either chemical doping or external pressure. Under applied high pressure (HP), materials undergo direct structural evolutions including the shortening of metal-ligand bond length, the distortions in the nearest neighbor environment, and the introduction of stress. These structural evolutions make HP significant in the researches on SCs, and many unanticipated.
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