High pressure raman study of Bi-2212

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.

Keywords:

• Raman
• Phonons
• High Pressure
• Superconductors
• Bi2sr2cacu2o8