POSITRON-ANNIHILATION STUDY OF THE ELECTRON-STRUCTURE OF LAB6 AND CEB6

We measured the two-dimensional angular correlation of the positron an nihilation radiation (2D-ACAR) on a single crystal of LaB6 for two pro jections. The anisotropies of the 2D electron-positron momentum densit y were very similar to those observed for the isostructural heavy-ferm ion (HF) system CeB6 in the paramagnetic phase and consistent with tho se of the calculated electron-positron momentum density of LaB6. The s tandard Lock-Crisp-West (LCW) analysis was in reasonable agreement wit h the LCW folding of the calculated 2D-ACAR spectrum and the de Haas-v an Alphen findings. From the projected k-space density we could evalua te. the Fermi volume, corresponding to 1.10+/-0.04 electrons per formu la unit, and deduce that the effect of the nonuniform positron density does not play a significant role. The apparent discrepancy with the L CW analysis of CeB6, where filtering procedures were required to recov er a k-space density similar to that obtained for LaB6, is discussed. [S0163-1829(97)02339-4].