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 (Formula presented.) 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 (Formula presented.) direction). The obtained structure is in agreement with quantum oscillation measurements and previous band structure calculations. For the isostructural topologically nontrivial (Formula presented.), the similar ellipsoids are connected through necks that have significantly smaller radii in the case of (Formula presented.). A theoretical analysis of the 2D-ACAR spectra is also conducted for (Formula presented.) 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 (Formula presented.) and (Formula presented.) are topologically trivial correlated metals.