Phonons in MgB2 by polarized Raman scattering on single crystals

Abstract

This paper presents a detailed Raman scattering study of the unusually broad ${E}_{2g}$ phonon mode in ${\mathrm{MgB}}_{2}$ crystal. It is shown by polarized Raman scattering on a few-micron-size crystallites with natural faces that the observed broad Raman feature really does obey the selection rules of an ${E}_{2g}$ mode. Raman spectra on high quality polycrystalline superconducting ${\mathrm{MgB}}_{2}$ wires reveal a very symmetric ${E}_{2g}$ phonon line near $615 {\mathrm{cm}}^{\ensuremath{-}1}$ with the room temperature linewidth of $260 {\mathrm{cm}}^{\ensuremath{-}1}$ only. Additional scattering of different polarization dependence, observed in certain crystallites, is interpreted as weighted phonon density of states induced by lattice imperfections.