KONDO RESONANCE IN THE NEUTRON-SPECTRA OF INTERMEDIATE-VALENT YBAL3

We have measured the dynamic susceptibility of intermediate-valent YbAl{sub 3} by means of cold-neutron scattering. We find two intense magnetic excitations below 40 meV. One of these, with location around 18 meV at helium temperatures, shifts steadily toward 0 meV with increasing temperatures. While crystal field interactions are unable to account for such a behavior, this excitation is in good agreement with a transition from the {ital f} ground state to a Kondo resonance as described by the Anderson model. In particular, it definitely excludes a gaplike magnetic response with gap width {Delta}=30 meV as asserted earlier.