The real part of the optical conductivity was calculated by using the Kubo formula approach, and in the framework of the 2-band model. It was shown that a single-gap model was insufficient to describe the optical behavior of superconductor MgB2 film, but the 2-gap model with different symmetries was sufficient to explain the experimental results.

Low-Temperature Dependence of the Optical Conductivity in Superconductor MgB2. M.A.Shahzamanian, H.Yavary, M.Moarrefi: Physica B, 2005, 358[1-4], 103-8