Stripe antiferromagnetic correlations in LaFeAsO_{1−x}F_{x} probed by ^{75}As NMR

Abstract

The anisotropy of the nuclear spin-lattice relaxation rate 1/T1 of 75As was investigated in the iron pnictide LaFeAs(O1−xFx) (x=0.07, 0.11, and 0.14) as well as LaFeAsO. While the temperature dependence of the normal-state 1/T1T in the superconducting (SC) x=0.07 is different from that in the SC x=0.11, their anisotropy of 1/T1, R≡(1/T1)H∥ab/(1/T1)H∥c in the normal state is almost the same (≃1.5). The observed anisotropy is ascribable to the presence of the local stripe correlations with Q=(π,0) or (0,π). In contrast, 1/T1 is isotropic and R is approximately 1 in the overdoped x=0.14 sample, where superconductivity is almost suppressed. These results suggest that the presence of the local stripe correlations originating from the nesting between hole and electron Fermi surfaces is linked to high-Tc superconductivity in iron pnictides.