Superconductivity-induced resonant Raman scattering in multilayer high-Tc superconductors -: art. no. 054509

Resonant Raman scattering below T-c has been discovered in several Bi-, Hg-, and Tl-based high-T-c superconductors with three or four CuO2 layers. For Bi2Si2Ca2Cu3O10+delta, we found an unexpected crossover of the pair-breaking peak in the A(1g) spectrum from a broad bump at homega=6k(B)T(c) for E-exc=2.54 eV to a sharp peak at homega=8k(B)T(c) for E-exc=2.18 eV, together with a strong enhancement of the Ca phonons. Under resonant conditions, the relative positions of the pair breaking peaks in A(1g), B-1g, and B-2g channels are 2Delta(A(1g))=2Delta(B-1g)>2Delta(B-2g). This relation implies that the A(1g) Raman channel is free from the Coulomb screening effect, just as predicted theoretically for a d-wave multilayer superconductor but have never been observed experimentally thus far. The observed resonance effect is evidence that the electronic state in the inner CuO2 planes is different from that of the outer CuO2 planes.