Raman study of Bi2−xPbxSr2Can−1CunO4+2n+δ (n=2,3) superconductors

Abstract

We report a Raman study of the n=2 and n=3 Bi2−xPbxSr2Can−1CunO4+2n+δ high-temperature superconducting cuprates. We find that the frequency of the O(2)Sr A1g mode systematically decreases with additional oxygen in the weakly coupled BiO layers. We speculate that this could be due to an expansion of the Cu-O-Bi bond length caused by an oxygen-induced compression of the weakly coupled BiO layers. It is shown that approximately one half of the decrease in the frequency of the O(2)Sr A1g mode in Bi2Sr2Ca1−zYzCu2O8+δ reported by Kahihana et al. can be attributed to the effect of additional oxygen and hence charge transfer effects are negligible for this Raman mode. The effect of Pb on the frequency of the O(2)Sr A1g mode, while being systematic, can not be explained. We attribute the small increase in hole concentration with increasing Pb concentration to a partial charge compensation by a reduction in oxygen content. We provide evidence that the 655 cm−1 peak can be attributed to apical oxygen sites at the boundaries of the supercell induced by the incommensurate modulation in the BiO layers.

Source-reported materials — not catalogue approval

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