Evolution of the optical spectrum with doping in iron pnictides Ba(Fe1-xCox)2As2

TL;DR

This study examines how doping affects the optical spectrum of Ba(Fe1-xCox)2As2, revealing the evolution of electronic properties and the interplay between magnetism and superconductivity.

Contribution

It provides a detailed analysis of the optical conductivity components and their relation to doping, magnetism, and superconductivity in iron pnictides.

Findings

Drude weight increases with doping

Incoherent spectral weight remains doping independent

Magnetic order correlates with a gap in the incoherent component

Abstract

We investigated the optical spectrum of Ba(Fe1-xCox)2As2 single crystals with various doping levels. It is found that the low-energy optical conductivity spectrum of this system can be decomposed into two components: a sharp Drude term and a broad "incoherent" term. For the compounds showing magnetic order, a gap appears predominantly in the "incoherent" component, while an s-wave like superconducting gap opens in both components for highly doped compounds. The Drude weight steadily increases as doping proceeds, consistent with electron doping in this system. On the other hand, the "incoherent" spectral weight is almost doping independent, but its spectral feature is intimately connected with the magnetism. We demonstrate that the presence of two distinct components in the optical spectrum well explains the doping and temperature dependences of the dc resistivity.