A High-Tc Mechanism of Iron Pnictide Superconductivity due to Cooperation of Ferro-orbital and Antiferromagnetic Fluctuations

Abstract

The electronic states and superconductivity in iron pnictides are studied on the basis of the 16 band $d$-$p$ model which includes both the onsite Coulomb interaction between Fe $d$ electrons and the intersite one between Fe $d$ and pnictogen $p$ electrons. The model well accounts for experimentally observed two fluctuations: the $d$-$d$ interaction-enhanced antiferromagnetic (AFM) fluctuation and the $d$-$p$ interaction-enhanced ferro-orbital (FO) fluctuation responsible for the $C_{66}$ elastic softening. The AFM fluctuation induces the repulsive pairing interaction for $\mathbf{q}\sim {\mathbf{Q}}_{\mathrm{AF}}$ while the FO does the attractive one for $\mathbf{q}\sim 0$ resulting in the $s_{\pm }$-wave superconductivity where the two fluctuations cooperatively enhance the superconducting transition temperature $T_c$ without any competition by virtue of the $\mathbf{q}$-space segregation.

4 pages, 4 figures

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• Structure of the pairing gap from orbital nematic fluctuations
• Thermodynamic electric quadrupole moments of nematic phases from first-principles calculation
• Fermi surface, pressure-induced antiferromagnetic order, and superconductivity in FeSe
• Nodal versus nodeless superconductivity in iso-electronic LiFeP and LiFeAs