Superconducting Gap Structure in Out-of-plane-disordered Bi2Sr2CaCu2O8+δ as Studied by Raman Spectroscopy

We measured electronic Raman spectra of nonstoichiometric Bi2+xSr2−xCaCu2O8+δ with x=0.1, 0.3 and stoichiometric Bi2Sr2Y0.08Ca0.92Cu2O8+δ and investigated the effect of out-of-plane disorder on the superconducting B1 g Raman response. We observed that the B1 g peak energy is enhanced in Y-substituted Bi2212, compared with that in nonstoichiometric Bi2212. By contrast, for nonstoichiometric Bi2212, the B1 g peak energy remains constant, even if Tc is significantly suppressed by disorder. This anomalous behavior is discussed in terms of the interplay between the pseudogap and superconducting gap.