Experimental evidence of Tc enhancement without the influence of spin fluctuations:NMR study on LaFeAsO1-x Hx under a pressure of 3.0 GPa

Abstract

The electron-doped high-transition-temperature (Tc) iron-based pnictide superconductor LaFeAsO1−xHx has aunique phase diagram: Superconducting double domes aresandwiched by antiferromagnetic phases at ambient pressure and they turn into a single dome with a maximum Tc that exceeds 45 K at a pressure of 3.0 GPa. We studied whether spin fluctuations are involved in increasing Tc under a pressure of 3.0 GPa by using the ⁷⁵As nuclear magnetic resonance (NMR) technique. The ⁷⁵As-NMR results for the powder samples show that Tc increases up to 48 K without the influence of spin fluctuations. This fact indicates that spin fluctuations are not involved in raising Tc, which implies that other factors, such as orbital degrees of freedom, may be important for achieving a high Tc of almost 50 K.