Positron annihilation study of the electronic structure ofLaB6andCeB6

Abstract

We measured the two-dimensional angular correlation of the positron annihilation radiation (2D-ACAR) on a single crystal of ${\mathrm{LaB}}_{6}$ for two projections. The anisotropies of the 2D electron-positron momentum density were very similar to those observed for the isostructural heavy-fermion (HF) system ${\mathrm{CeB}}_{6}$ in the paramagnetic phase and consistent with those of the calculated electron-positron momentum density of ${\mathrm{LaB}}_{6}.$ The standard Lock-Crisp-West (LCW) analysis was in reasonable agreement with the LCW folding of the calculated 2D-ACAR spectrum and the de Haas--van Alphen findings. From the projected $\mathit{k}$-space density we could evaluate the Fermi volume, corresponding to $1.10\ifmmode\pm\else\textpm\fi{}0.04$ electrons per formula unit, and deduce that the effect of the nonuniform positron density does not play a significant role. The apparent discrepancy with the LCW analysis of ${\mathrm{CeB}}_{6},$ where filtering procedures were required to recover a $\mathit{k}$-space density similar to that obtained for ${\mathrm{LaB}}_{6},$ is discussed.