Fermi Surface Modeling of Light-Rare-Earth Hexaborides using Positron Annihilation Spectroscopy

2D angular correlation of the positron annihilation radiation (2D-ACAR) spectra are measured for LaB6 along high-symmetry directions and compared with first-principles calculations based on density functional theory (DFT). This allows the modeling of the Fermi surface in terms of ellipsoid electron pockets centered at X-points elongated along the sigma axis (Gamma-M direction). The obtained structure is in agreement with quantum oscillation measurements and previous band structure calculations. For the isostructural topologically nontrivial SmB6, the similar ellipsoids are connected through necks that have significantly smaller radii in the case of LaB6. A theoretical analysis of the 2D-ACAR spectra is also conducted for CeB6 including the on-site repulsion U-correction to the local density approximation (LDA+U) of the DFT. The similarities of the 2D-ACAR spectra and the Fermi surface projections of these two compounds allow to infer that both LaB6 and CeB6 are topologically trivial correlated metals.