New hot topic in ARPES on HTSC, the observation of the so called "waterfalls", is addressed. The energy scale at about 0.2-0.3 eV that can be derived from the coherent component of ARPES spectra measured along the nodal direction is not new but has been already discussed in terms of a coupling to a bosonic continuum. However, the waterfalls, namely the long vertical parts of the experimental dispersion around the center of the Brillouin zone (BZ), seem to be purely artificial. They are a consequence of simple matrix-element effect: a complete suppression of the photoemission intensity from both the coherent and "incoherent" components. When the matrix-elements are taken into account, the latter reveals a grid-like structure along the bonding directions in the BZ.
@article{arxiv.cond-mat/0702374,
title = {"Waterfalls" in cuprates},
author = {A. A. Kordyuk and S. V. Borisenko and D. Inosov and V. B. Zabolotnyy and J. Fink and B. Buechner and R. Follath and V. Hinkov and B. Keimer and H. Berger},
journal= {arXiv preprint arXiv:cond-mat/0702374},
year = {2007}
}