Relation between Superconducting Gap Minima and Nesting Vector in   YNi2B2C
  We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy to directly observe the large superconducting (SC) gap anisotropy (GA) of YNi2B2C. The result shows large SC GA with a smooth variation along an intersection of a Fermi surface (FS) around the $\Gamma$-Z line and nearly isotropic SC gap values for two intersections of FSs around the X-P line but with a point-like non-zero minimum only for one sheet. The point-like SC gap minimum can be connected by the nesting vector reported from band calculations. The results show unexpectedly complicated SC GA of borocarbide superconductors. 
T. Baba, T. Yokoya, S. Tsuda, T. Watanabe, M. Nohara, H. Takagi T.   Oguchi and S. Shin