Fermi Surface Study of LaRu2Si2 and of Heavy-Fermion CeRu2Si2 above the Kondo Temperature

The Two-dimensional (2D) angular correlation of the positron annihilation radiation of the heavy-fermion system CeRu 2 Si 2 was measured above the Kondo temperature T K and compared to that of the reference isostructural non-f-electron system LaRu 2 Si 2 . The k-space densities of the two compounds, obtained via the Lock-Crisp-West folding of the 3D-reconstructed electron-positron momentum densities, were very similar. These results are in reasonable agreement with the hand structure calculated for CeRu 2 Si 2 using the local-density approximation (LDA). Conversely, in the case of LaRu 2 Si 2 . a clear discrepancy between the LDA calculation and the experiment appears unless the Fermi level (E F ) is raised by ∼1 I mRy After the E F adjustment the calculated Fermi surfaces are rather similar and in agreement with both experiments. The implications of this similarity on the physics of the heavy fermions are discussed.