Non-Fermi-Liquid Transport Phenomena and Superconductivity Driven by Orbital Fluctuations in Iron Pnictides: Analysis by Fluctuation-Exchange Approximation

TL;DR

This paper investigates how orbital fluctuations in iron pnictides influence their transport and superconducting properties, revealing a link between orbital dynamics and different superconducting states.

Contribution

It provides a unified analysis of normal and superconducting states driven by orbital fluctuations using the FLEX approximation.

Findings

Orbital fluctuations lead to linear or convex temperature dependence of resistivity.

An s++-wave superconducting state emerges when orbital fluctuations dominate.

Competition between orbital and spin fluctuations results in a nodal s-wave state.

Abstract

We study the five-orbital Hubbard model including the charge quadrupole interaction for iron pnictides. Using the fluctuation-exchange (FLEX) approximation, orbital fluctuations evolve inversely proportional to the temperature, and therefore the resistivity shows linear or convex T-dependence for wide range of temperatures. We also analyze the Eliashberg gap equation, and show that s-wave superconducting state without sign reversal (s++ -wave state) emerges when the orbital fluctuations dominate over the spin fluctuations. When both fluctuations are comparable, their competition gives rise to a nodal s-wave state. The present study offers us a unified explanation for both the normal and superconducting states.