Double-Q spin-density wave in iron arsenide superconductors

摘要: Elucidating the nature of magnetic ground state iron-based superconductors is paramount importance in unveiling mechanism behind their high-temperature superconductivity. Until recently, it was thought that superconductivity emerges only from an orthorhombic antiferromagnetic stripe phase, which can principle be described terms either localized or itinerant spins. However, we recently reported tetragonal symmetry restored inside magnetically ordered certain hole-doped compounds, revealing existence a new phase at compositions close to onset Here, present Mossbauer data show half iron sites this are non-magnetic, establishing conclusively novel with non-uniform magnetization inconsistent Instead, naturally explained as interference between two commensurate spin-density waves, rare example collinear double-Q order. Our results demonstrate character magnetism pnictides, and primary role played by degrees freedom determining phase diagram. A combination neutron scattering, X-ray scattering spectroscopy experiments reveal ordering arsenide superconductor.