Anomalous dispersion in the autocorrelation of angle-resolved photoemission spectra of high-temperature Bi2 Sr2 Ca Cu2 O8+δ superconductors

We find that peaks in the autocorrelation of angle-resolved photoemission spectroscopy data of Bi2 Sr2 Ca Cu2 O8+δ in the superconducting state show dispersive behavior for binding energies smaller than the maximum superconducting energy gap. For higher energies, though, a striking anomalous dispersion is observed that is a consequence of the interaction of the electrons with collective excitations. In contrast, in the pseudogap phase, we only observe dispersionless behavior for the autocorrelation peaks. The implications of our findings in regard to Fourier transformed scanning tunneling spectroscopy data are discussed.