Eliashberg Analysis of Optical Spectra Reveals Strong Coupling of Charge Carriers to Spin Fluctuations in Superconducting Iron Pnictides

TL;DR

This study uses Eliashberg analysis of optical spectra in iron-based superconductors to demonstrate that spin fluctuations strongly couple to charge carriers, mediating superconductivity, with spectral features evolving with temperature.

Contribution

It provides direct evidence linking spin fluctuations to charge carrier coupling in iron pnictides through optical spectroscopy and Eliashberg formalism analysis.

Findings

Peak in spectral density around 10 meV matches spin resonance energies.

Spectral density evolves with temperature towards a less structured background.

Strong coupling between spin fluctuations and charge carriers is confirmed.

Abstract

The temperature and frequency dependences of the optical conductivity of Co and Ni-doped BaFe2As2 are analyzed and the electron-boson spectral density a2F(w) extracted using Eliashberg's formalism. The characteristic energy of a large peak in the spectrum around 10 meV coincide with the resonance peak in the spin excitation spectra, giving compelling evidence that in iron-based superconductors spin fluctuations strongly couple to the charge carriers and mediate superconductivity. In addition the spectrum is found to evolve with temperature towards a less structured background at higher energies as in the spin susceptibility.