Tc enhancement under pressure in the La1111 pnictide LaFeAsO1-xHx (x=0.2) studied by NMR

Abstract

Nuclear magnetic resonance (NMR) measurements under a pressure of 3.0 GPa were performed for a prototypical iron-based high-Tc superconductor LaFeAsO1-xHx (x=0.2). At ambient pressure, this compound has superconducting (SC) double domes with the Tc 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 Tc minimum at x=0.2 goes up to 45 K, the Tc maximum, at 3.0 GPa. Despite that Tc enhancement under pressure was confirmed from the 75As relaxation rate divided by temperature (T), 1/T1Taround Tc, 1/T1Tat 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-xFx, suggesting that spin fluctuations are not essential to achieve high Tc over 45 K.