Strong electronic correlations in iron pnictides: Comparison of the optical spectra for BaFe2As2-related compounds

TL;DR

This study investigates the optical spectra of BaFe2As2-related compounds, revealing that iron pnictides exhibit strong electronic correlations and incoherent charge dynamics, which are linked to their superconducting properties.

Contribution

It provides a comparative analysis of optical spectra across different pnictides, highlighting the role of electronic correlations and structural factors in their charge dynamics.

Findings

Iron arsenides show highly incoherent charge dynamics.

The degree of coherence correlates with bond angle and electron filling.

Strong correlations are linked to superconductivity emergence.

Abstract

We carried out combined transport and optical measurements for BaFe2As2 and five isostructural transition-metal (TM) pnictides. The low-energy optical conductivity spectra of these compounds are, to a good approximation, decomposed into a narrow Drude (coherent) component and an incoherent component. The iron arsenides, BaFe2As2 and KFe2As2, are distinct from other pnictides in their highly incoherent charge dynamics or bad metallic behavior with the coherent Drude component occupying a tiny fraction of the low-energy spectral weight. The fraction of the coherent spectral weight or the degree of coherence is shown to be well correlated with the TM-pnictogen bond angle and the electron filling of TM 3d orbitals, which are measures of the strength of electronic correlations. The iron arsenides are thus strongly correlated systems, and the doping into BaFe2As2 controls the strength of electronic correlations. This naturally explains a remarkable asymmetry in the charge dynamics of electron- and hole-doped systems, and the unconventional superconductivity appears to emerge when the correlations are fairly strong.