Electronic structure and anisotropic superconductivity in diborides and borocarbides

Abstract

We compare calculated Fermi surface sheet (FSS) areas F and masses of MgB 2 and ZrB 2 with dHvA data. Deviations in F in MgB 2 can be removed by a small mutual shift of σ- and π bands. The dHvA masses lead to orbit averaged el–ph coupling constants λ ̄ σ ≈1.03 and λ ̄ π ≈0.32 , while for ZrB 2 only λ ̄ <0.1 holds. The anisotropy of the Fermi velocities and the orbital character of various FSS of rare earth (R) transition metal (T) borocarbides RT 2B 2C, their relationship to the H c2-anisotropy, and the coexistence of magnetism and superconductivity are discussed.