Evidence for two superconducting gaps in MgB2 - art. no. 157002

We have measured the Raman spectra of polycrystalline MgB2 from 25 to 1200 cm(-1). A superconductivity-induced redistribution in the electronic Raman continuum was observed. Two pair-breaking peaks appear in the spectra, sugg esting the presence of two superconducting gaps. The measured spectra were analyzed using a quasi-two-dimensional model in which two s-wave supercondu cting gaps open on two sheets of Fermi surface. For the gap values we have obtained Delta (1) = 22 cm(-1) (2.7 meV) and Delta (2) = 50 cm(-1) (6.2 meV ). Our results suggest that a conventional phonon-mediated pairing mechanis m occurs in the planar boron sigma bands and is responsible for the superco nductivity of MgB2.