ESR Study of the Kondo Effect inAu:Yb

Paramagnetic resonance experiments at 3 and 9 GHz were performed in dilute $Au:\mathrm{Yb}$ in the temperature range from 100 mK to 4 K. All results show for the first time a logarithmic temperature dependence for the $g$-value shift and for the relaxation rate in complete agreement with theoretical predictions. The fit yields a Kondo temperatue of $T_{\mathrm{K}}\sim 10$ μK and a degeneracy of $d\sim 3$ for the local-moment-conduction-electron interaction channels.