Theoretical study of correlation between spin fluctuations and T_c in isovalent-doped 1111 iron-based superconductors

摘要

Motivated by recent experiments on isovalent-doped 1111 iron-based superconductors LaFeAs_(1-x)P_xO_(1-y)F_y and the theoretical study that followed, we investigate, within the five-orbital model, the correlation between spin fluctuations and the superconducting transition temperature, which exhibits a double-dome feature upon varying the Fe-As-Fe bond angle. Around the first dome with higher T_c, the low-energy spin fluctuation and T_c are not tightly correlated because the finite-energy spin fluctuation also contributes to superconductivity. On the other hand, the strength of the low-energy spin fluctuation originating from the d_(xz/yz) orbital is correlated with T_c in the second dome with lower T_c. These calculation results are consistent with a recent NMR study, and hence strongly suggest that the pairing in iron-based superconductors is predominantly caused by multiorbital spin fluctuations.