Electric and magnetic properties of LaFeAsO_1-xH_x under pressure

The electron-doped high-transition-temperature (T_c) iron-based pnictide superconductor LaFeAsO_1-xH_x has a unique phase diagram: superconducting (SC) double domes are sandwiched by antiferromagnetic (AF) phases at ambient pressure and transform to a single dome with a maximum T_c that exceeds 45 K at high pressures. We investigated the evolution of the SC phase upon applying pressure via resistivity measurements, and also the relationship between superconductivity and AF fluctuations from nuclear magnetic resonance measurements. Results suggest that the single dome is presumably a consequence of the effective merging of the double domes and that AF fluctuations are not involved in increasing T_c. (author)