Abstract
The coexistence of magnetic and nonmagnetic phases in the superconducting potassium iron selenide, KxFe2-ySe2, has been intensely debated. With superconductivity proposed to appear in a stoichiometric, nonmagnetic phase with I4/mmm crystal symmetry, the proposed nonsuperconducting phase is magnetic and has a lower symmetry, I4/m. The latter consists of Fe vacancies that go through a disordered-to-ordered transition in which the partially filled Fe sites create a supercell upon ordering. We show, using neutron scattering on the optimally doped composition, K0.8Fe2-ySe2, that the absence of magnetism does not signal the presence of superconductivity. Moreover, the degree of vacancy order is coupled to the strength of the magnetic order. Superconductivity coincides with the presence of the magnetic order parameter, albeit the latter is significantly weaker than previously reported, contradicting the current understanding of this ∼30K superconductor.
| Original language | English |
|---|---|
| Article number | 024503 |
| Journal | Physical Review B |
| Volume | 94 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jul 5 2016 |
Funding
The authors would like to acknowledge valuable discussions with W. Bao, T. Egami, A. Bianconi, and W. Ku. The work at the University of Virginia was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. DE-FG02-01ER45927, and that at Oak Ridge National Laboratory, by the Office of Basic Energy Sciences, Division of Scientific User Facilities. The work at NIST was supported by the US Department of Commerce.