Doping-dependent evolution of the electronic structure of (formula presented) in the superconducting and metallic phases

The electronic structure of the (formula presented) (LSCO) system has been studied by angle-resolved photoemission spectroscopy (ARPES). We report on the evolution of the Fermi surface, the superconducting gap, and the band dispersion around the extended saddle point (formula presented) with hole doping in the superconducting and metallic phases. As hole concentration x decreases, the flat band at (formula presented) moves from above the Fermi level (formula presented) for (formula presented) to below (formula presented) for (formula presented) and is further lowered down to (formula presented) From the leading-edge shift of ARPES spectra, the magnitude of the superconducting gap around (formula presented) is found to monotonically increase as x decreases from (formula presented) down to (formula presented) even though (formula presented) decreases in the underdoped region, and the superconducting gap appears to smoothly evolve into the normal-state gap at (formula presented) It is shown that the energy scales characterizing these low-energy structures have similar doping dependences. For the heavily overdoped sample (formula presented) the band dispersion and the ARPES spectral line shape are analyzed using a simple phenomenological self-energy form, and the electronic effective mass enhancement factor (formula presented) has been found. As the hole concentration decreases, an incoherent component that cannot be described within the simple self-energy analysis grows intense in the high-energy tail of the ARPES peak. Some unusual features of the electronic structure observed for the underdoped region (formula presented) are consistent with numerical works on the stripe model.