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 Σ axis (Γ-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 are topologically trivial correlated metals.