The first study was made here of the optical conductivity of MgB2, covering the range of its lowest-energy superconducting gap. Teraherz time-domain spectroscopy was used to determine the complex frequency-dependent conductivity of thin films. The imaginary part revealed an inductive response due to the emergence of the superconducting condensate. The real part exhibited a strong depletion of oscillator strength near to 5meV; resulting from the opening of a superconducting energy gap. The gap ratio of approximately 1.9 was well below the weak-coupling value; pointing to a complex behavior in this superconductor.

Far-Infrared Optical Conductivity Gap in Superconducting MgB2 Films. R.A.Kaindl, M.A.Carnahan, J.Orenstein, D.S.Chemla, H.M.Christen, H.Y.Zhai, M.Paranthaman, D.H.Lowndes: Physical Review Letters, 2002, 88[2], 027003 (3pp)