Anisotropic quasiparticle scattering rates in slightly underdoped to optimally doped high-temperature LSCO superconductors

An angle-resolved photoemission study of the scattering rate in the superconducting phase of the high-temperature superconductor LSCO 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 $E_1sim0.4$ eV. The scattering rate is found to be strongly anisotropic, with a minimum along the (0,0)-($pi,pi$) direction. A possible connection to a quantum-critical point is discussed.