  75As-nuclear magnetic resonance (NMR) on an iron-based superconductor
LaFeAsO1-xFx (x=0.14) was performed under a pressure of 3GPa. Enhancement of
superconducting transition temperature Tc was confirmed from the relaxation
rate 1/T1; Tc goes up to 40K by applying pressure up to 3GPa. 1/T1T, which is
temperature independent just above Tc and gives a measure of the density of
states (DOS) at the Fermi energy, enhances by applying pressure. These facts
suggest that the increase of the DOS leads to the enhancement of Tc. On the
other hand, anomalous behavior of 1/T1T observed at high temperatures is
suppressed by applying pressure.
