  We report on infrared studies of charge dynamics in a prototypical pnictide
system: the BaFe2As2 family. Our experiments have identified hallmarks of the
pseudogap state in the BaFe2As2 system that mirror the spectroscopic
manifestations of the pseudogap in the cuprates. The magnitude of the infrared
pseudogap is in accord with that of the spin-density-wave gap of the parent
compound. By monitoring the superconducting gap of both P- and Co-doped
compounds, we find that the infrared pseudogap is unrelated to
superconductivity. The appearance of the pseudogap is found to correlate with
the evolution of the antiferromagnetic fluctuations associated with the
spin-density-wave instability. The strong-coupling analysis of infrared data
further reveals the interdependence between the magnetism and the pseudogap in
the iron pnictides.
