Evidence for two distinct energy scales in the Raman spectra of YBa2(Cu1-xNix)3O6.95.

We report electronic Raman scattering from Ni-substituted YBa2Cu3O6.95 single crystals with T(c) ranging from 92.5 to 78 K. The fully symmetrical A(1g) channel and the B(1g) channel which is sensitive to the d(x(2)-y(2)) gap maximum have been explored. The energy of the B(1g) pair-breaking peak remains constant under Ni doping while the energy of the A(1g) peak scales with T(c) ( E(A(1g))/k(B)T(c) = 5). Our data show that the A(1g) peak tracks the magnetic resonance peak observed in inelastic neutron scattering yielding a key explanation to the long-standing problem of the origin of the A(1g) peak.