Two-band conductivity of a FeSe₀.₅Te₀.₅ film by reflectance measurements in the terahertz and infrared range

الأصل · EN

We report an infrared spectroscopy study of a 200 nm thick FeSe₀.₅Te₀.₅ film grown on LaAlO₃ with Tc=13.7 K. We analyze the 20 K normal state absolute reflectance Rₙ measured over a broad infrared range and the reflectance ratio Rₛ/Rₙ, Rₛ being the superconducting state reflectance, measured at 6 K in the terahertz range down to 12 cm⁻¹. We show that the normal state model conductivity is given by two Drude components, one of which much broader and intense than the other. In the superconducting state, we find that a gap Δ=37±3 cm⁻¹ opens up in the narrow Drude band only, while the broad Drude band results to be ungapped, at least in the explored spectral range. Our results show that only a two-band model can coherently describe both normal and superconducting state data.