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.
We investigated the temperature- and frequency-dependent optical scattering rates in the pseudogap phase of cuprates using model pseudogap and electron-boson spectral density (EBSD) functions. We obtained the scattering rates at various temperatures below and above a given pseudogap temperature using a generalized Allen’s (or Sharapov’s) formula, which has been used to analyze the measured optical spectra of correlated electron systems with a non-constant density of states at finite temperatures. The pseudogap and EBSD functions should be temperature dependent to simulate the Fermi liquid-like behaviour of underdoped cuprate systems observed in optical studies. Therefore, the observed Fermi liquid-like behaviour can be understood by considering the combined contribution from the T-dependent EBSD function and the T-dependent pseudogap. We expect that our results will aid in understanding the Fermi liquid-like optical response in the pseudogap phase and in revealing the microscopic pairing mechanism for superconductivity in cuprates.
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