Enhancement of Tc Due to Pressure Application in LaFeAsO1–xHx Studied by NMR

The prototypical iron-based high-Tc pnictide LaFeAsO1–xHx has superconducting double domes in the electronic phase diagram. Pressure application merges the double domes into a single dome, and the minimum Tc of 26K observed at x=0.2 goes up to 45K by applying a pressure of 3.0GPa. 75As nuclear magnetic resonance was performed at 3.0GPa to investigate the high-Tc mechanism. The relaxation rate divided by temperature, 1/T1T exhibits a plateau just above Tc and the value is enhanced by applying pressure. The plateau indicates that 1/T1 can be described by the Korringa relation, which suggests that a key factor to raise Tc is the density of states. So far as our results are concerned, spin fluctuations are not essential to achieve high Tc over 45K.