Quantitative Raman measurement of the evolution of the Cooper-pair density with doping in Bi2Sr2CaCu2O8+δ superconductors

We report Raman measurements on Bi2Sr2CaCu2O8+delta single crystals that allow us to quantitatively evaluate the doping dependence of the density of Cooper pairs in the superconducting state. We show that the drastic loss of Cooper pairs in the antinodal region as the doping level is reduced is concomitant with a deep alteration of the quasiparticles dynamic above T-c and consistent with a pseudogap that competes with superconductivity. Our data also reveal that the overall density of Cooper pairs evolves with doping, distinctly from the superfluid density above the doping level p(c)=0.2.