Electronic structure of Ni-substituted Y(Ni(1-x)M(x))(2)B2C superconductors

The substitution of Ni by the transition metals Fe, Co, and Ru in YNi2B2C is analyzed using the self-consistent local-density embedded-cluster approach. Changes of partial densities of states, charge density, and bond order are examined to elucidate bonding structure and the interplay between covalent, ionic, and metallic interactions in these highly anisotropic superconductors. Impurity induced modifications in distribution and composition of states near the Fermi level are discussed in terms of the observed drop in T-c with impurity concentration. Electric-field gradients are obtained at the central site. In the case of iron substitution with concentration x less than or equal to 0.1, electric quadrupole splitting is compared with Mossbauer experimental results.