<研究ノート>鉄系高温超伝導体LaFeAsO[1-x]Fxの高圧下核磁気共鳴測定

Abstract

The relationship between spin fluctuation and superconductivity has been investigated in La1111 series, LaFeAsO[1_x]Fx(x = 0, 0.05, 0.08, 0.10, and 0.14) via nuclear magnetic resonance (NMR) at both ambient pressure and high pressure (3.0 GPa). The results shows that the critical doping level at which low-frequency spin fluctuation vanishes is around the optimally doped regime (x~0.10), and Tc remarkably increases in overdoped regime (x=0.14) by applying pressure, implying that the spin fluctuation is not important to the high-Tc mechanism. The x dependence of Tc at 3.0 GPa is similar to that of Ln1111 (Ln = Ce, Pr, Sm, etc.) with high Tc above 40 K at ambient pressure, indicating that pressure application is equivalent to full rare-earth substitution. The equivalence suggests that high Tc above 40 K is realized when the spin fluctuation is absent.