⁷⁵As-NMR studies on LaFeAsO _1-xF _x (x = 0:14) under a pressure of 3 GPa

⁷⁵As-nuclear magnetic resonance (NMR) on an iron (Fe)-based superconductor LaFeAsO _1-xF _x (x = 0:14) was performed under a pressure of 3 GPa. Enhancement of the superconducting transition temperature (T _c) was confirmed from the relaxation rate (1=T ₁); T _c goes up to 40K by applying pressure up to 3 GPa. 1=T ₁T, which is temperature independent just above T _c and gives a measure of the density of states (DOS) at the Fermi energy, enhances by applying pressure. These facts suggest that an increase of the DOS leads to the enhancement of T _c. On the other hand, anomalous behavior of 1=T ₁T observed at high temperatures is suppressed by applying pressure.