Observation of a van Hove Singularity in $Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$ with Angle Resolved Photoemission

摘要

We have performed high energy resolution angle-resolved photoemission studiesof 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 saddlepoint 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 boththe $\Gamma-\bar{M}-Z$ and perpendicular directions.