75As-NMR Studies of LaFeAsO1-xFx for Various x Values

الأصل · EN

Results of 75As NMR and NQR measurements are reported for superconducting samples of LaFeAsO1-xFx with various x values. The x dependent widths of the superconducting transition and those of the NQR spectra indicate that the optimally doped LaFeAsO1-xFx sample with the superconducting transition temperature Tc 28 K has the smallest width or smallest inhomogeneity of the superconducting order parameter Δ. In the analyses of the temperature (T) dependence of the NMR longitudinal relaxation rate 1/T1, we have tried to use a simple relation 1/T1 Tⁿ to see how fast 1/T1 decreases when the superconducting order parameter grows. The relation holds rather well in the T region of 0.3Tc < T =< Tc, and n varies from 2.5-6 with varying x, having the maximum value 5-6 at the optimal x. These results indicate that the x dependence of n originates from the spatial distribution of Δ, and that the T⁵⁻⁶ behavior is considered to be intrinsic to this system.