Pressure-induced quantum critical behavior in LaFeAsO1-xHx studied via NMR

Abstract

LaFeAsO1-xHx is a prototypical iron-based superconductor. However, its phase diagram presents unique properties compared to conventional iron-based superconductors: (1) the superconducting phase is sandwiched between two antiferromagnetic (AF) phases appearing in lightly (x ≤ 0.05) and heavily (0.49 ≤ x) H-doped regimes. (2) The AF phase (0.49 ≤ x) is strongly suppressed when applying pressure. We measured the relaxation time T1 at 75As sites for x=0.6 under pressures up to 3.7 GPa to investigate the behavior near the quantum critical point (QCP). The relaxation rate divided by temperature (T) 1/T1T exhibited a peak at the AF transition temperature (TN) followed by Curie-Weiss behavior at low temperatures below TN.. The result demonstrates that the gapped excitation originating from the spin-density-wave state and the gapless excitation characteristic to the QCP coexist near the pressure-induced QCP.