Line-shape analysis of the Raman-spectrum from B1g bond buckling phonon in Bi2Sr2CaCu2O8+x

We performed Raman spectroscopy on two different over-doped Bi2Sr2CaCu2O8+x (BSCCO), of which superconducting transition temperatures are 89 K and 77 K. Line-shape analysis of the Raman-spectrum was done, focused on B1g bond buckling mode which have drawn a lot of attention, since photoemission studies showed an evidence for strong coupling between the mode and electron. The line-shapes show asymmetry and are well fitted by the Fano line-shape formula. Remarkably, we found that the peak line-widths from B1g bond buckling mode in BSCCO show much broader than those in YBa2Cu3O7−x. The broad line width can be attributed to the superstructure modulation of BSCCO. Our results imply that B1g bond buckling mode may have close relation to the origin of superconductivity or to boosting the superconducting transition temperature in BSCCO.