Bosonic spectrum of a correlated multiband system, BaFe1.80Co0.20As2, obtained via infrared spectroscopy

Abstract We investigated a single crystal BaFe2-xCoxAs2 (Co-doped BaFe2As2: Co-Ba122) to obtain a bosonic spectrum using infrared spectroscopy. We used the generalized Allen formula, an extended Drude-Lorentz model for the normal state, and a two-parallel-channel approach for the superconducting (SC) state to obtain the bosonic spectrum from the optical conductivity. This analysis required a couple of Lorentz modes at very low-energy, but these modes were not necessary to analyze the K-doped BaFe2As2 (K-Ba122) and LiFeAs. Various physical quantities, such as the coupling constant, maximum SC transition temperature, SC coherence length, and upper critical field, were extracted from the bosonic spectrum. The superfluid plasma frequency and the London penetration depth were also obtained from the optical conductivity. The physical properties of Co-Ba122 and K-Ba122 were also compared and discussed in this study. We believe that our results will be helpful in figuring out the microscopic pairing mechanism for superconductivity in doped Ba122 systems and will provide useful information on their applications.