Evidence for the Single-Site Quadrupolar Kondo Effect in the Dilute Non-Kramers System Y1-xPrxIr2Zn20

Acoustic signatures of the single-site quadrupolar Kondo effect in Y0.966Pr0.034Ir2Zn20 are presented. The elastic constant (C-11 - C-12)/2, corresponding to the Gamma(3)(E)-symmetry electric-quadrupolar response, reveals a logarithmic temperature dependence of the quadrupolar susceptibility in the low-magnetic-field region below similar to 0.3 K. Furthermore, the Curie-type divergence of the elastic constant down to similar to 1 K indicates that the Pr ions in this diluted system have a non-Kramers ground-state doublet. These observations evidence the single-site quadrupolar Kondo effect, as previously suggested based on specific-heat and electrical-resistivity data