Doping dependence of the gap anisotropy of the high-temperatureYBa2Cu3O7−δsuperconductor

Abstract

We have performed high-resolution angle-resolved photoemission spectroscopy of ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ with various hole concentrations from under-to-optimal doping. We have determined the momentum dependence of bulk superconducting gap as a function of hole concentration and found the enhancement of antinodal gap, the deviation from simple ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ wave, and the reduction of superconducting coherence weight in the underdoped region. We also found the universality of the doping dependence of the SC-gap size and symmetry in bilayered cuprates. These results suggest the importance of the long-range pairing interactions in the underdoped region.