Doping-dependent evolution of the electronic structure ofLa2−xSrxCuO4in the superconducting and metallic phases

Abstract

The electronic structure of the ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ (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 $\mathbf{k}=(\ensuremath{\pi},0)$ with hole doping in the superconducting and metallic phases. As hole concentration x decreases, the flat band at $(\ensuremath{\pi},0)$ moves from above the Fermi level ${(E}_{\mathrm{F}})$ for $x>0.2$ to below ${E}_{\mathrm{F}}$ for $x<0.2,$ and is further lowered down to $x=0.05.$ From the leading-edge shift of ARPES spectra, the magnitude of the superconducting gap around $(\ensuremath{\pi},0)$ is found to monotonically increase as x decreases from $x=0.30$ down to $x=0.05$ even though ${T}_{c}$ decreases in the underdoped region, and the superconducting gap appears to smoothly evolve into the normal-state gap at $x=0.05.$ It is shown that the energy scales characterizing these low-energy structures have similar doping dependences. For the heavily overdoped sample $(x=0.30),$ 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 ${m}^{*}{/m}_{b}\ensuremath{\simeq}2$ 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 $(x\ensuremath{\lesssim}0.10)$ are consistent with numerical works on the stripe model.