Observation of a van Hove Singularity in   $Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$ with Angle Resolved Photoemission
  We have performed high energy resolution angle-resolved photoemission studies of the normal state band structure of oxygen overdoped $Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$. We find that there is an extended saddle point singularity in the density of states along $\Gamma-\bar{M}-Z$ direction. The data also indicate that there is an asymmetry in the Fermi surface for both the $\Gamma-\bar{M}-Z$ and perpendicular directions. 
Jian Ma, C.Quitmann, R.J.Kelley, P.Alm\'eras, H.Berger, G.   Margaritondo, and M.Onellion (Dept.of Phys. & ASC, UW-Madison a...