The Raman spectra of polycrystalline material were measured from 25 to 1200/cm. A superconductivity-induced redistribution in the electronic Raman continuum was observed. Two pair-breaking peaks appear in the spectra, suggesting the presence of 2 superconducting gaps. The measured spectra were analyzed by using a quasi 2-dimensional model in which 2 s-wave superconducting gaps opened onto 2 sheets of Fermi surface. For the gap values, It was found that Δ1 = 22/cm (2.7meV) and Δ2 = 50/cm (6.2meV). The results suggested that a conventional phonon-mediated pairing mechanism occurred in the planar B σ-bands and was responsible for the superconductivity.

Evidence for Two Superconducting Gaps in MgB2. X.K.Chen, M.J.Konstantinovic, J.C.Irwin, D.D.Lawrie, J.P.Franck: Physical Review Letters, 2001, 87[15], 157002 (3pp)