Nuclear-magnetic-resonance measurements of an iron (Fe)-based superconductor LaFeAsO1-xFx (x=0.08 and 0.14) were performed at ambient pressure and under pressure. The relaxation rate 1/ T 1 for the overdoped samples (x=0.14) shows T -linear behavior just above Tc, and pressure application enhances 1/T1 T similar to the behavior of Tc This implies that 1/T1 T=constant originates from the Korringa relation, and an increase in the density of states at the Fermi energy D (EF) leads to the enhancement of Tc. In the underdoped samples (x=0.08), 1/ T1 measured at ambient pressure also shows T -linear behavior in a wide temperature range above Tc. However, 1/ T1 T shows Curie-Weiss-type T dependence at 3.0 GPa accompanied by a small increase in Tc, suggesting that predominant low-frequency antiferromagnetic fluctuation is not important for development of superconductivity or remarkable enhancement of Tc. The qualitatively different features between underdoped and overdoped samples are systematically explained by a band calculation with hole and electron pockets.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2010 Mar 22|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics