We report a systematic study by As75 nuclear-quadrupole resonance in LaFeAsO 1-xF x. The antiferromagnetic spin fluctuation found above the magnetic ordering temperature T N=58K for x=0.03 persists in the regime 0.04≤x≤0.08, where superconductivity sets in. A dome-shaped x dependence of the superconducting transition temperature T c is found, with the highest T c=27K at x=0.06, which is realized under significant antiferromagnetic spin fluctuation. With increasing x further, the antiferromagnetic spin fluctuation decreases, and so does T c. These features resemble closely the cuprates La 2-xSr xCuO 4. In x=0.06, the spin-lattice relaxation rate (1/T 1) below T c decreases exponentially down to 0.13T c, which unambiguously indicates that the energy gaps are fully opened. The temperature variation of 1/T 1 below T c is rendered nonexponential for other x by impurity scattering.
ASJC Scopus subject areas
- Physics and Astronomy(all)