Disentangling superconducting and magnetic orders in NaFe1-xNixAs using muon spin rotation

Article

关键词: IRON-BASED SUPERCONDUCTORS;    PENETRATION DEPTH;    APPROXIMATION;    VISUALIZATION;    RELAXATION;    ANISOTROPY;    NEMATICITY;    DYNAMICS;    SYMMETRY;    DENSITY;   

DOI  :  10.1103/PhysRevB.97.224508

来源: SCIE

【 摘 要 】

Muon spin rotation and relaxation studies have been performed on a 111 family of iron-based superconductors, NaFe1-xNixAs, using single crystalline samples with Ni concentrations x = 0, 0.4, 0.6, 1.0, 1.3, and 1.5%. Static magnetic order was characterized by obtaining the temperature and doping dependences of the local ordered magnetic moment size and the volume fraction of the magnetically ordered regions. For x = 0 and 0.4%, a transition to a nearly-homogeneous long range magnetically ordered state is observed, while for x greater than or similar to 0.4% magnetic order becomes more disordered and is completely suppressed for x = 1.5%. The magnetic volume fraction continuously decreases with increasing x. Development of superconductivity in the full volume is inferred fromMeissner shielding results for x greater than or similar to 0.4%. The combination ofmagnetic and superconducting volumes implies that a spatially-overlapping coexistence of magnetism and superconductivity spans a large region of the T - x phase diagram for NaFe1-xNixAs. A strong reduction of both the ordered moment size and the volume fraction is observed below the superconducting T-C for x = 0.6, 1.0, and 1.3%, in contrast to other iron pnictides in which one of these two parameters exhibits a reduction below T-C, but not both. The suppression of magnetic order is further enhanced with increased Ni doping, leading to a reentrant nonmagnetic state below T-C for x = 1.3%. The reentrant behavior indicates an interplay between antiferromagnetism and superconductivity involving competition for the same electrons. These observations are consistent with the sign-changing s(+/-) superconducting state, which is expected to appear on the verge of microscopic coexistence and phase separation with magnetism. We also present a universal linear relationship between the local ordered moment size and the antiferromagnetic ordering temperature T-N across a variety of iron-based superconductors. We argue that this linear relationship is consistent with an itinerant-electron approach, in which Fermi surface nesting drives antiferromagnetic ordering. In studies of superconducting properties, we find that the T = 0 limit of superfluid density follows the linear trend observed in underdoped cuprates when plotted against T-C. This paper also includes a detailed theoretical prediction of the muon stopping sites and provides comparisons with experimental results.

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