Microscopic Coexistence of Superconductivity and Magnetism in Ba_{1-x}K_{x}Fe_{2}As_{2} (original) (raw)

2011, Physical Review Letters

We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of Ba(Fe1−xRux)2As2 (x = 0.23). We find two phase transitions, to antiferromagnetism at TN ≈ 60 K and to superconductivity at TC ≈ 15 K. Below TN , our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4 µB/Fe. The spin-lattice relaxation rate 1/ 75 T1 is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below TC, 1/ 75 T1 on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity. In the iron-based superconductors, superconductivity (SC) is achieved on suppressing a long-ranged antiferromagnetic order [1] by doping or pressure. At this phase boundary, much attention has been drawn to the question of whether SC may coexist with antiferromagnetism (AFM). Proposals for possible coexisting phases have included commensurate [2] and incommensurate [3-5] magnetic structures, competition between AFM and SC , and variations in the size of the ordered moment or the pairing symmetry . No consensus has yet been reached on the pairing mechanism or the possible phenomena arising from the interplay of AFM and SC. For most materials, local-probe studies on high quality samples are required as a matter of urgency to distinguish the key properties of microscopic coexistence from any form of phase separation.

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