Temperature dependence of the Raman spectra for Bi2CaSr2Cu2O8

We report an anomaly at Tc ( 85 K) in the temperature dependence of the A1g phonon mode at 464 cm-1 in Bi2CaSr2Cu2O8. It behaves similarly to the B1g phonon mode previously found in YBa2Cu3O7. However, the anomalously behaving phonon reported here has two different characteristics. First, it has a considerably higher energy than the B1g phonon, and hence should be considerably higher in energy than the superconducting band gap. Second, this phonon involves motion primarily of the oxygen atoms above and below the Cu-O planes rather than those in the Cu-O planes as is the case for the B1g phonons in YBa2Cu3O7. © 1989 The American Physical Society.