Effect of nonmagnetic impurities on the gap of a d(x)2-(y)2 superconductor as seen by angle-resolved photoemission

An analysis of angle-resolved photoemission (ARPES) experiments in the superconducting state of the high-T-c copper oxides is presented. It is based on a phenomenological weak-coupling BCS model which incorporates the experimental normal-state dispersion extracted from ARPES. and nonmagnetic impurity scattering in the presence of a d(x2-y2) Order parameter (OF). It is shown that already in the pure case, the broadening by finite momentum resolution of the analyzer leads to a finite region of apparent ''gaplessness'' around the true node of the OF. Nonmagnetic impurities further amplify this effect by introducing additional spectral weight around zero frequency. At sufficiently large impurity concentrations n(i) approximate to 0.02-0.05, this results in an extended region of gaplessness up to delta phi=+/-7 (phi the angle on the Fermi surface) around the true node for a large range of moderate to strong impurity potential strengths. Different ways to identify the presence of impurity scattering in the ARPES spectra are proposed.