Optical spectroscopy of superconducting Ba{0.55}K{0.45}Fe2As2: evidence for strong coupling to low energy bosons

TL;DR

Optical spectroscopy of Ba0.55K0.45Fe2As2 reveals strong coupling between charge carriers and low-energy bosons, indicating a possible pairing mechanism in this iron-based superconductor.

Contribution

This study provides detailed optical spectra analysis showing strong low-energy bosonic coupling in Ba0.55K0.45Fe2As2, offering insights into its superconducting pairing mechanism.

Findings

Charge carriers interact with a broad bosonic spectrum peaking at 25 meV.

The coupling constant decreases from approximately 2 at low temperature to 0.6 at ambient temperature.

The scattering rate saturates at 150 meV, lower than in cuprates.

Abstract

Optical spectroscopy on single crystals of the new iron arsenide superconductor Ba{0.55}K{0.45}Fe2As2 shows that the infrared spectrum consists of two major components: a strong metallic Drude band and a well separated mid infrared absorption centered at 0.7 eV. It is difficult to separate the two components unambiguously but several fits of Lorentzian peaks suggest a model with a Drude peak having a plasma frequency of 1.8 to 2.1 eV and a midinfrared peak with a plasma frequency of 2.5 eV. In contrast to the cuprate superconductors the scattering rate obtained from the extended Drude model saturates at 150 meV as compared to 500 meV for a typical cuprate. Detailed analysis of the frequency dependent scattering rate shows that the charge carriers interact with broad bosonic spectrum with a peak at 25 meV and a coupling constant lambda =approx 2 at low temperature. As the temperature increases this coupling weakens to lambda=0.6 at ambient temperature. This suggests a bosonic spectrum that is similar to what is seen in the lower Tc cuprates.