I've mentioned this "kink" before in the ARPES spectrum on high-Tc superconductors. However, if you want a rather brief overview of the issues surrounding ARPES data (and interpretation) of this kink structure, don't miss the current issue of Science 25 November 2005, Vol. 310, p. 1271. This was the area of physics that I worked till about 3 years ago. Zz.