  The oxygen dopant concentration dependence of the "quasiparticle" feature at
600-750 cm-1 of the infrared spectrum of Bi2Sr2CaCu2O8+delta (BSCCO), lying
near and above the top of the host phonon spectrum at 600 cm-1, is strongly
correlated with superconductivity. Using parameter-free topological methods,
theory assigns this feature to split apical oxygen interstitials. It explains
both the qualitative similarities and the quantitative differences between
"quasiparticle" features identified in infrared and phtoemission data, as well
as identifying new features in the infrared spectra.
