Investigations of the relationship between T_c and the superconducting gap under magnetic and nonmagnetic impurity substitutions in YBa_2Cu_3O_(7-δ)

摘要

We report electronic Raman scattering measurements on optimally doped YBa_2Cu+3O7_(7-δ) 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.