Magnetic excitations in a single crystal of the Kondo semiconductor YbB12

Inelastic neutron-scattering measurements have been performed on a single crystal of the Kondo semiconductor YbB12 by using a triple-axis spectrometer. We have found two magnetic excitations; one is dispersive from 14 to 20 meV and the other centered at 37 meV is less dispersive. The excitation energy of the former agrees with the gap energy derived from the specific heat and transport measurements. With increasing temperature, both excitations disappear at 60 K, above which a quasi-elastic peak and another peak centered around 25 meV appear. (C) 1999 Elsevier Science Ltd. All rights reserved.