NMR Study on a Pnictide Superconductor LaFeAsO1−x H x in a H-Overdoped Regime: Revival of Antiferromagnetic Fluctuations

Abstract

An electron-doped high-T c pnictide LaFeAsO1−x H x is recently known for having double superconducting (SC) domes in the phase diagram. We have performed nuclear magnetic resonance (NMR) measurements in an H-overdoped regime to investigate the second SC dome on a microscopic level. We unexpectedly discovered that the linewidths of both 75As and 1H spectra broaden at low temperatures for the 58 and 62.5 % H-doped samples, indicating that the antiferromagnetic (AF) ordering returns in the heavily H-doped regime. The finding itself is rare because an excess carrier doping tends to cause Fermi-liquid behavior in strongly correlated electron systems. We demonstrate that the new AF ordering originates from the nesting between electron pockets.