Kondo resonance in the neutron spectra of intermediate-valentYbAl3

Abstract

We have measured the dynamic susceptibility of intermediate-valent ${\mathrm{YbAl}}_3$ 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 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 Δ=30 meV as asserted earlier.