Band structure calculations and Fermi surfaces of YNi2B2C

To clarify the anisotropic gap behavior of YNi2B2C, energy band structures and Fermi surfaces are calculated by using an FLAPW method. The de Haas-van Alphen frequencies and the cyclotron masses are compared with the experimental results. The comparison between those masses shows that the electron-phonon interactions depend on the orbits. It is found that a multiply connected Fermi surface contributes dominantly to the superconductivity and the saddle-point singularity of the band is expected to lead an anisotropic gap behavior in YNi2B2C