Universal Decomposition of the Low-Frequency Conductivity Spectra of Iron-Pnictides Uncovering Fermi-Liquid Behavior

TL;DR

Infrared spectroscopy of 122 iron-pnictides uncovers two electronic subsystems, revealing Fermi-liquid behavior in the superconducting state and distinct temperature-dependent and independent contributions to conductivity.

Contribution

This study provides a universal decomposition method for low-frequency conductivity spectra, highlighting Fermi-liquid behavior in iron-pnictides.

Findings

Hidden T^2 dependence in resistivity indicates Fermi-liquid state.

Two electronic subsystems identified with distinct temperature behaviors.

Incoherent background persists across all compounds, influenced by superconductivity.

Abstract

Infrared reflectivity measurements on 122 iron-pnictides reveal the existence of two electronic subsystems. The one gapped due to the spin-density-wave transition in the parent materials, such as EuFe$_2$As$_{2}$, is responsible for superconductivity in the doped compounds, like Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$. Analyzing the dc resistivity and scattering rate of this contribution, a hidden $T^2$ dependence is found, indicating that superconductivity evolves out of a Fermi-liquid state. The second subsystem gives rise to incoherent background, present in all 122 compounds, which is basically temperature independent, but affected by the superconducting transition.