TUBULAR FERMI SURFACES IN TRANSITION-METAL SUPERLATTICES

Calculations of the Fermi surfaces of Co/Ni (001) and (111) superlatti ces, based on a tight-binding model and on a Green function approach, reveal that superlattice Fermi surfaces have a tubular structure with a highly anisotropic cylindrical topology. The superlattice potential changes the cubic symmetry of Co and Ni and leads to undulating multis heeted cylindrical Fermi surfaces with marked two-dimensional characte r and strong nesting in both perpendicular and growth directions. The uncommon superlattice topology may result in unique properties. In par ticular, large anisotropic transport coefficients and electronic insta bilities associated to coupled points on the Fermi surface are expecte d.