Fermi surface of CeCu2Si2 by 2D angular correlation of positron annihilation radiation

We have carried out 2D angular correlation of positron annihilation radiation measurements on oriented single crystals of the heavy-fermion superconductor CeCu2Si2. Measurements have been made at 50 and 4 K which are above and below the Kondo temperature, T-K similar to 15 K, for this compound. The measurements show a small temperature dependence. Experimental results have been compared with linear muffin-tin orbital band-structure calculations for CeCu2Si2 and the isostructural non-f-electron compound, LaCu2Si2, The measured anisotropies agree well with the calculations. In addition, at both temperatures, the measured [001] projected k-space occupation densities reflect clearly the Fermi-surface breaks predicted by the calculations for CeCu2Si2. This implies that local-density approximation calculations provide a good description of the electronic structure in CeCu2Si2. We have also measured the positron lifetime in both superconducting (S-type) and magnetic (A-type) samples of CeCu2Si2. The lifetime and intensity components in the S- and A-type polycrystals are different, suggesting that the nature of the defects that trap positrons is different in the two phases.