Doping-dependent Evolution of the Electronic Structure of La2-xSrxCuO4 in the Superconducting and Metallic Phases

TLDR: The electronic structure of the LSCO system has been studied by angle-resolved photoemission spectroscopy (ARPES) as discussed by the authors, where the authors report on the evolution of the Fermi surface, the superconducting gap, and the band dispersion around the extended saddle point with hole doping in the super-conducting 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 $xg0.2$ to below ${E}_{\mathrm{F}}$ for $xl0.2,$ 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.