Fermi-Surface Modeling of Light-Rare-Earth Hexaborides with 2D-ACAR Spectroscopy

TL;DR

This study uses 2D-ACAR spectroscopy and DFT calculations to model the Fermi surfaces of light-rare-earth hexaborides, revealing their topologically trivial metallic nature and structural similarities.

Contribution

It provides the first detailed Fermi surface modeling of LaB6 and CeB6 using 2D-ACAR spectroscopy combined with DFT, including correlation effects for CeB6.

Findings

Fermi surface modeled as ellipsoid electron pockets in LaB6

Agreement with quantum oscillation measurements and prior calculations

Both LaB6 and CeB6 are topologically trivial correlated metals

Abstract

Two dimensional angular correlation of the positron annihilation radiation (2D-ACAR) spectra are measured for $\mathrm{LaB}_6$ along high symmetry directions and compared with first principle 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 not-trivial $\mathrm{SmB}_6$ the similar ellipsoids are connected through necks that have significantly smaller radii in the case of $\mathrm{LaB}_6$. A theoretical analysis of the 2D-ACAR spectra is also performed for $\mathrm{CeB}_6$ including the on-site repulsion $U$ correction to the local-density approximation (LDA+$U$) of the DFT. The similarities of 2D-ACAR spectra and the Fermi-surface projections of these two compounds allow to infer that both $\mathrm{LaB}_6$ and $\mathrm{CeB}_6$ are topologically trivial correlated metals.