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 (formula presented) was measured above the Kondo temperature (formula presented) and compared to that of the reference isostructural non-(formula presented)-electron system (formula presented) The (formula presented)-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 band structure calculated for (formula presented) using the local-density approximation (LDA). Conversely, in the case of (formula presented) a clear discrepancy between the LDA calculation and the experiment appears unless the Fermi level (formula presented) is raised by (formula presented) After the (formula presented) 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. © 2002 The American Physical Society.