The electronic structure of the ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (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 $\mathbf{k}=(\pi ,0)$ with hole doping in the superconducting and metallic phases. As hole concentration x decreases, the flat band at $(\pi ,0)$ moves from above the Fermi level ${(E}_{\mathrm{F}})$ for $x>\mathrm{}0.2\mathrm{}$ to below $E_{\mathrm{F}}$ for $x<\mathrm{}0.2,$ and is further lowered down to $x=\mathrm{0.05.}\mathrm{}$ From the leading-edge shift of ARPES spectra, the magnitude of the superconducting gap around $(\pi ,0)$ is found to monotonically increase as x decreases from $x=0.30\mathrm{}$ down to $x=0.05\mathrm{}$ even though $T_c$ decreases in the underdoped region, and the superconducting gap appears to smoothly evolve into the normal-state gap at $x=\mathrm{0.05.}\mathrm{}$ It is shown that the energy scales characterizing these low-energy structures have similar doping dependences. For the heavily overdoped sample $\mathrm{}(x=0.30\mathrm{}),$ 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 $m^{*}{/m}_b\simeq 2$ 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 $(x\lesssim 0.10)$ are consistent with numerical works on the stripe model.

• Received 23 May 2000

DOI:https://doi.org/10.1103/PhysRevB.65.094504