Abstract
We measured the elastic constants (C11 − C12)/2 and C44 of the non-Kramers system Y0.63Pr0.37Ir2Zn20 (Pr-37\% system) by means of ultrasound to check how the single-site quadrupolar Kondo effect is modified by increasing the Pr concentration. The Curie-like softening of (C11 − C12)/2 of the present Pr-37\% system on cooling from 5 to 1 K can be reproduced by a multipolar susceptibility calculation based on the non-Kramers Γ3 doublet crystalline-electric-field ground state. Further, on cooling below 0.15 K, a temperature dependence proportional to \(T \) was observed in (C11 − C12)/2. This behavior rather corresponds to the theoretical prediction of the quadrupolar Kondo “lattice” model, unlike that of the Pr-3.4\% system, which shows a logarithmic temperature dependence based on the “single-site” quadrupolar Kondo theory. In addition, we discuss the possibility to form a vibronic state by the coupling between the low-energy phonons and the electric quadrupoles of the non-Kramers doublet in the Pr-37\% system, since we found a low-energy ultrasonic dispersion in the temperature range between 0.15 and 1 K.
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