NMR Study Under Pressure on the La1111 Pnictides, LaFeAsO 1− x F x
The relationship between antiferromagnetic (AF) fluctuation and superconductivity was investigated in the La1111 series, LaFeAsO1−x
(x=0.05, 0.08, and 0.14) by examining nuclear relaxation rates (1/T
1) at both ambient pressure and 3.0 GPa. Although the AF fluctuation is enhanced by applying pressure in the underdoped regime
(x=0.05, and 0.08), the increase in critical transition temperature (T
c) is small, whereas T
c increases remarkably in the overdoped regime (x=0.14) where the AF fluctuation is absent, suggesting that high T
c above 40 K originates not from the AF fluctuation but from the density of states at the electron pocket.