Investigations of the relationship between Tc and the superconducting gap under magnetic and nonmagnetic impurity substitutions in YBa2Cu3O7-δ

We report electronic Raman scattering measurements on optimally doped YBa2Cu3O7-delta where Zn or Ni impurities have been substituted by Cu. Using Raman selection rules, we have probed the superconducting gap in the nodal and antinodal regions. We show that under impurity substitutions, the energy of the antinodal peak detected in the superconducting state is not related to the critical temperature T-c and that signatures of superconductivity disappear in the nodal regions. Our experimental findings advocate in favor of gapless arcs around the nodes. The breakdown of the relationship between the antinodal gap amplitude and T-c is discussed in terms of local superconducting gap and pseudogap.