The MgB2 superconducting energy gaps measured by Raman spectroscopy

Understanding the nature of the superconducting energy gap in magnesium diboride is an essential part of understanding this unusual superconductor, and Raman scattering is a convenient and powerful technique which is able to directly measure the key physical properties of the gap. The Raman spectra of MgB2 show clear superconductivity induced renormalisations and evidence is found for two superconducting gaps residing on the sigma and pi Fermi surfaces with maximum magnitudes of around 110 and 30 cm(-1). The larger gap appears as a sharp peak in the electronic Raman scattering continuum while the smaller gap manifests itself as a threshold in the low-frequency spectral intensity, indicating that the gaps form in different electronic environments. The physical properties of the gaps favour explanations of the extraordinarily high T-c in MgB2, within strong coupling theory. (C) 2002 Elsevier Science B.V. All rights reserved.