  It has been noted that certain surfaces of Weyl semimetals have bound states
forming open Fermi arcs, which are never seen in typical metallic states. We
show that the Fermi arcs enable them to support an even more exotic surface
state with crossed flat bands in the superconducting state. We clarify the
topological origin of the crossed flat bands and the relevant symmetry that
stabilizes the cross point. We also discuss their possible experimental
verification by tunneling spectroscopy.
