We present angle-resolved photoemission spectroscopy data on moderately underdoped La1.855Sr0.145CuO4 at temperatures below and above the superconducting transition temperature. Unlike previous studies of this material, we observe sharp spectral peaks along the entire underlying Fermi surface in the superconducting state. These peaks trace out an energy gap that follows a simple d-wave form, with a maximum superconducting gap of 14 meV. Our results are consistent with a single gap picture for the cuprates. Furthermore our data on the even more underdoped sample La1.895Sr0.105CuO4 also show sharp spectral peaks, even at the antinode, with a maximum superconducting gap of 26 meV.

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An angle-resolved photoemission study of the scattering rate in the superconducting phase of the high-temperature superconductor La2−xSrxCuO4 with x = 0.145 and x = 0.17, as a function of binding energy and momentum, is presented. We observe that the scattering rate scales linearly with binding energy up to the high-energy scale E1 ∼ 0.4 eV. The scattering rate is found to be strongly anisotropic, with a minimum along the (0,0)-(π, π) direction. A possible connection to a quantum-critical point is discussed.