c-Axis Electronic Raman Scattering inBi2Sr2CaCu2O8+δ

We report on the $c$-axis-polarized electronic Raman scattering of $\mathrm{Bi}{}_2\mathrm{Sr}{}_2\mathrm{CaCu}{}_2\mathrm{O}{}_{8+\delta }$ single crystals with various oxygen concentrations. In the normal state, a resonant electronic continuum extends to 1.5 eV and gains significant intensity as the incoming photon energy increases. Below $T_c$, a superconductivity-induced $2\Delta$ peak is observed for $\omega <80\mathrm{}\mathrm{meV}$ and the $2\Delta {/k}_B{T}_c$ value increases with decreasing hole doping. In particular, this $A_{1g}$ $2\Delta$ peak energy, which is higher than that seen with in-plane polarizations for all doping levels studied, signifies distinctly different dynamics of quasiparticles created with out-of-plane polarization.