Giant Electron-Phonon Anomaly in Doped and Other Cuprates
Figure 7
(a) Displacement patterns of zone-boundary bond-stretching modes in cuprates. Top: longitudinal mode in the [110] direction (breathing mode); middle: transverse mode in the [110]-direction (quadrupolar mode); bottom: longitudinal mode in the [100] direction (half-breathing mode). Circles and full points represent oxygen and copper atoms, respectively. Only the displacements in the Cu–O planes are shown. All other displacements are small for these modes. (b) Schematic of the doping dependence of the breathing and half-breathing zone boundary mode frequencies. This behavior is probably not directly related to the mechanism of superconductivity, since the softening continues into the overdoped nonsuperconducting part of the phase diagram from [30].
