Magnetic excitons in a topological Kondo insulator candidate YbB₁₂

We employed time-of-flight inelastic neutron scattering to investigate magnetic excitations in the topological Kondo insulator (TKI) candidate YbB₁₂. Covering the entire Brillouin zone, our data reveal two resonant modes and a continuum all with weak dispersion and a pronounced Q-dependent oscillator strength. The Q-dependence of the intensity of the resonant modes at hω ≈ 40 meV and hω ≈ 15 meV, corresponds to dynamic antiferromagnetic correlations between the nearest and next-nearest Yb neighbors, respectively. Neither mode exhibits intensity at the Γ point. The resonant modes appear to represent collective excitons within the d-f hybridization gap. We utilized the Anderson lattice model with phenomenological tight-binding band structures to simulate the Q-dependence of these magnetic excitons to obtain an experimental measure of the electronic band structure. We also report the field dependence or the 15 meV exciton for fields along the [110].