Doping dependence of many-body effects along the nodal direction in the high-T_c cuprate (Bi,Pb)₂Sr₂CaCu₂O₈

Angle-resolved photoemission spectroscopy (ARPES) is used to study the doping dependence of the lifetime and the mass renormalization of the low-energy excitations in high-T_c cuprate (Bi,Pb)₂Sr₂CaCu₂O₈ along the zone diagonal. We find a linear energy dependence of the scattering rate for the underdoped samples and a quadratic energy dependence for the overdoped case. The mass enhancement of the quasiparticles due to the many body effects at the Fermi energy is found to be in the order of 2 and the renormalization extends over a large energy range for both the normal and the superconducting state. The much discussed kink in the dispersion around 70 meV is interpreted as a small additional effect at low temperatures.