A Novel Large Moment Antiferromagnetic Order in K _0.8 Fe _1.6 Se ₂ Superconductor

TLDR

The discovery of cuprate high‑Tc superconductors has spurred the search for unconventional superconductors in magnetic materials, where suppressing long‑range order in a magnetic parent compound by doping or pressure often drives the system toward a quantum critical point. The authors report an exception to this rule in the recently discovered potassium iron selenide. They identified the superconducting composition as the iron‑vacancy‑ordered K₀.₈₃Fe₁.₆₄Se₂ with Tc > 30 K and observed a large‑moment antiferromagnetic order (3.31 μB/Fe) with an unprecedented ordering temperature TN ≈ 559 K. The study suggests a staggeringly polarized electronic density of states, implying that superconductivity in this material occurs under a strong spin‑exchange field and merits further investigation.

Abstract

The discovery of cuprate high TC superconductors has inspired the search for unconventional superconductors in magnetic materials. A successful recipe has been to suppress long-range order in a magnetic parent compound by doping or high pressure to drive the material towards a quantum critical point. We report an exception to this rule in the recently discovered potassium iron selenide. The superconducting composition is identified as the iron vacancy ordered K0.83(2)Fe1.64(1)Se2 with TC above 30 K. A novel large moment 3.31 μB/Fe antiferromagnetic order that conforms to the tetragonal crystal symmetry has an unprecedentedly high ordering temperature TN ≈ 559 K for a bulk superconductor. Staggeringly polarized electronic density of states is thus suspected, which would stimulate further investigation into superconductivity in a strong spin-exchange field under new circumstances.