NMR Study Under Pressure on the La1111 Pnictides, LaFeAsO1−x F x

Abstract

The relationship between antiferromagnetic (AF) fluctuation and superconductivity was investigated in the La1111 series, LaFeAsO1−x F 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.