Structural properties and band structure of heavy fermion systems: CeCu2Si2 and LaCu2Si2

The structure of CeCu₂Si₂, isotypic with ThCr₂Si₂, has been refined in a single-crystal study. The atomic parameters were used in self-consistent LMTO band structure calculations for CeCu₂Si₂ and isostructural LaCu₂Si₂. The results are analysed in terms of energy levels, charge distribution and in particular Fermi surface properties. The Ce-4f levels are situated mainly aboveE _F , except near the Γ-point. The density-of-states atE _F is large and heavily concentrated around the Ce-4f band. This makes local Ce 4f fluctuations possible, while interaction with the rest of the band structure is small. The comparison with LaCu₂Si₂ shows that the additional Cef electron is partly promoted into the non-f bands. Large enhancement factors are required to bring band results into agreement with observed specific heat and magnetic critical field. Strong Fermi surface anisotropies are pointed out for both compounds suggesting new experiments on single crystals.