Superconducting order parameter in heavily overdoped $Bi_2 Sr_2 Ca Cu_2   O_{8+\delta}$: a global quantitative analysis
  A systematic analysis of the complex lineshape at $(\pi,0)$ of heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is presented. We show that a coherent component in the quasi-particle excitation is correlated with the superfluid density throughout the entire doping range and suggest it is a direct measure of the order parameter of high temperature superconductors. 
R. H. He, D. L. Feng, H. Eisaki, J.-i. Shimoyama, K. Kishio, G. D. Gu