Low-energy magnetic response and Yb valence in the Kondo insulator YbB12 -: art. no. 064411

X-ray absorption and high-resolution inelastic neutron-scattering experiments on the Kundo insulator YbB12 are reported. The ytterbium L-3-edge spectrum consists of a single white line with no observable temperature dependence between 10 and 295 K, indicating that the Yb valence is closer to 3+ than was concluded from previous high-resolution photoemission and XPS results. The neutron measurements confirm the existence of a gap in the magnetic excitation spectrum for T=5 K, and show that its gradual suppression as temperature increases is due to thr appearance of an extra quasielastic component in the: magnetic dynamical response.