We present optical transmission measurements that reveal a charge gap of 0.86 eV in the local moment antiferromagnetic insulator BaMn2As2, an order of magnitude larger than previously reported. Density functional theory plus dynamical mean field theory (DFT+DMFT) calculations correctly reproduce this charge gap only when a strong Hund's coupling is considered. Thus, BaMn2As2 is a member of a wider class of Mn pnictide compounds that are Mott-Hund's insulators. We also present optical reflectance for metallic 2% K doped BaMn2As2 that we use to extract the optical conductivity at different temperatures. The optical conductivity σ1(ω) exhibits a metallic response that is well described by a simple Drude term. Both σ(ω→0, T) and ρ(T) exhibit Fermi liquid temperature dependencies. From these measurements, we argue that a more strongly correlated Hund's metal version of the parent compounds of the iron pnictide superconductors has not yet been realized by doping this class of Hund's insulators.
@article{arxiv.1509.06759,
title = {From Hunds insulator to Fermi liquid: Optical spectroscopy study of K doping in BaMn$_2$As$_2$},
author = {D. E. McNally and S. Zellman and Z. P. Yin and K. W. Post and Hua He and K. Hao and G. Kotliar and D. Basov and C. C. Homes and M. C. Aronson},
journal= {arXiv preprint arXiv:1509.06759},
year = {2015}
}