Infrared studies of superconducting MgB2 thin films

Reflectance of superconducting MgB2 thin films (Tc≈35 K) has been measured in a broad spectral range from 30 to 110,000 cm−1. A typical plasma edge with a reflectance minimum at 15,000 cm−1 has been found. In the far-infrared region we observe a pronounced rise of the reflectance below 60 cm−1, which appears below Tc and can be associated with superconducting state. The temperature-dependent complex conductivity at infrared frequencies has been determined. The real and imaginary parts of the conductivity below Tc show a temperature evolution, which is characteristic for superconducting gap opening (decrease in σ1 and rise in σ2).