Investigation of the Superconducting Gap in MgB2 by Raman Spectroscopy

The Raman spectra of polycrystalline {\mgb} have been measured from 50 {\cm} to 1200 {\cm} at temperatures above and below $T_c$, using parallel and crossed polarization scattering geometries. When the temperature was decreased below $T_c$, a superconductivity induced redistribution in the electronic Raman continuum occurred at frequencies below 200 {\cm}. A pair-breaking peak at 110 {\cm} due to excitations across the superconducting gap appeared in both scattering geometries. The polarization independence of the peak frequency is consistent with an isotropic s-wave gap. The frequency of the pair breaking peak indicates $2\Delta \approx 4.1 k_BT_c$.