T c enhancement under pressure in the La1111 pnictide LaFeAsO 1-x H x (x=0.2) studied by NMR

Nuclear magnetic resonance (NMR) measurements under a pressure of 3.0 GPa were performed for a prototypical iron-based high-T c superconductor LaFeAsO1-x H x (x=0.2). At ambient pressure, this compound has superconducting (SC) double domes with the T c minimum of 26 K at x=0.2 in the electronic phase diagram. Pressure application merges the double domes into a single dome, and the T c minimum at x=0.2 goes up to 45 K, the T c maximum, at 3.0 GPa. Despite that T c enhancement under pressure was confirmed from the 75As relaxation rate divided by temperature (T), 1/T 1 Taround T c, 1/T 1 Tat high temperatures was almost the same with that at ambient pressure and hardly showed Cure-Weiss behaviour. These features are also seen for 14% F-doped LaFeAsO1-x F x , suggesting that spin fluctuations are not essential to achieve high T c over 45 K.