High pressure raman study of Bi-2212

Abstract

The hydrostatic pressure dependence of the Raman spectra of Bi2Sr2CaCu2O8 single crystals has been investigated. The energy of the A g and B 1g modes was found to increase with pressure in agreement with previously reported measurements, except the strong mode at ∼465 cm−1, which softens with pressure, while another peak at ∼458 cm−1 appears more pronounced at low temperatures and high pressures. The energy of both modes does not seem to change with increasing pressure, up to ∼5 GPa, although the average energy of the wide band has been found to soften, which is in disagreement with previously published results. Based on the modifications observed in some phonons at ∼1.8 GPa, which correlate with the reduction of T c and the deformations of the CuO5 pyramids, we attribute the mode at ∼465 cm−1 to the vibrations of the apex oxygen atoms. All modes due to the oxygen atoms were found to be strongly anharmonic.