Theoretical study on the correlation between the spin fluctuation and $T_c$ in the isovalent-doped 1111 iron-based superconductors

TL;DR

This study uses a five orbital model to explore how spin fluctuations relate to the superconducting transition temperature in isovalent-doped 1111 iron-based superconductors, revealing a double dome behavior and orbital-specific correlations.

Contribution

It provides a theoretical analysis of the correlation between spin fluctuations and $T_c$, highlighting the orbital dependence and the double dome feature in these materials.

Findings

Low-energy spin fluctuation correlates with $T_c$ in the second dome.

Finite energy spin fluctuation also contributes to superconductivity.

Results align with recent NMR experiments.

Abstract

Motivated by recent experiments on isovalent-doped 1111 iron-based superconductors LaFeAs$_{1-{x}}$P$_{x}$O$_{1-{y}}$F$_{y}$ and the theoretical study that followed, we investigate, within the five orbital model, the correlation between the spin fluctuation 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 recent NMR study, and hence strongly suggest that the pairing in the iron-based superconductors is predominantly caused by the multi-orbital spin fluctuation.