Normal-State Optical Response Functions of MgB2 Superconductor

The reflectivity of superconducting MgB2 (Tc = 39 K) has been measured on a randomly oriented thin film at room temperature over a wide-range of frequencies, 20 ≤ ω < 100000 cm−1. The conductivity shows highly metallic behavior but cannot be explained with a simple Drude model alone. The electronic contribution is analyzed by a generalized Drude model. The scattering rate 1/τ(ω) and the mass renormalization ratio m*(ω)/m = 1 + λ (ω) exhibit clear frequency dependence. The electron–phonon coupling strength is estimated to be λ ∼ 1.5 ± 0.5 while the plasma frequency ωp is 2.4 eV.