Lattice dynamics in the Kondo insulator YbB12

Energy dispersion of phonons in the Kondo insulator YbB12 (open symbols) and its structure analogue LuB12 (closed symbols). Circles: longitudinal branches; triangles: transverse branches. Lines represent the result of the model calculation based on assumption of a strong hierarchy of the interactions between boron and rare-earth (RE) atoms: B-B⪢B-RE⪢RE-RE. Irreducible representations of phonon branches are given in the Bouckaert-Smoluchowski-Wigner notation.