C-axis electronic Raman scattering in Bi_2Sr_2CaCu_2O_{8+\delta}
  We report a c-axis-polarized electronic Raman scattering study of Bi_2Sr_2CaCu_2O_{8+\delta} single crystals. In the normal state, a resonant electronic continuum extends to 1.5 eV and gains significant intensity as the incoming photon energy increases. In the superconducting state, a coherence 2\Delta peak appears around 50 meV, with a suppression of the scattering intensity at frequencies below the peak position. The peak energy, which is higher than that seen with in-plane polarizations, signifies distinctly different dynamics of quasiparticle excitations created with out-of-plane polarization. 
H.L. Liu, G. Blumberg, M.V. Klein, P. Guptasarma, and D.G. Hinks