Magnetic excitations in a single crystal of the Kondo semiconductor YbB12

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