We present experimental results of elastic constants as a function of temperature (T ) and magnetic field (H) for a single crystal of PrTi 2 Al 20 for the first time. A clear elastic softening was observed in the temperature dependence of elastic constants, C L =(C 11 +2C 12 +4C 44 )/3 and C T =(C 11 -C 12 +C 44 )/3, being suggestive of a remarkable fluctuation of quadrupolar moments O 20 and O 22 with Γ 3 symmetry. The elastic anomaly associated with a phase transition at 2.0 K exhibits the ferroquadrupolar (FQ) phase behavior under magnetic fields in accordance with the other physical properties such as magnetic susceptibility and specific heat. The softening can be explained well based on the crystalline electric field (CEF) effect model with a Γ 3 ground state. Furthermore, it was found that a coupling constant of the inter-site interaction between relevant quadrupolar moments is positive, indicating the FQ interaction mediated in this system. We argue the FQ scenario and 4 f multiplets of Pr 3+ split by CEF effect in PrTi 2 Al 20

We have investigated elastic properties of the mixed-valent intermetallic compound YbPd by means of ultrasonic measurements on the single-crystals. A pronounced elastic anomaly (elastic softening) was observed at around the transition temperature T 1 ≈130 K with a significant hysteresis, being indicative of a first-order phase transition. Furthermore, it was found that the elastic anomaly showing up around T 1 was hardly affected by application of a magnetic field, suggesting the non-magnetic origin. We can analyze quantitatively the temperature dependence of all measured elastic modes C 11 and C 44 with a Jahn-Teller formula. Our findings suggest that the pronounced elastic softening toward T 1 will enable us to predict the possible charge ordering origin.

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We report measurements of elastic constants detected close to a quantum critical point (QCP) of YbPtSb using one of the bestestablished macroscopic probes, ultrasonic method. The elastic constant shows a pronounced elastic softening toward zero temperature below around 20 K. It is noteworthy that these are not Curie type softening, which generally indicate a crystalline electric field (CEF) effect, but a logarithmic decrease of the elastic constant. Furthermore, with increasing magnetic field, the temperature range in which a logarithmic decrease of the elastic constant is observed shifts gradually to higher temperatures, suggesting a crossover from non-Fermi liquid to Fermi liquid tuned by an external field. We discuss the first observation of NFL effects and its magnetic field dependence at ambient pressure in a high-quality single crystal of an undoped Yb-based heavy fermion compound: YbPtSb. Yb Sb PtSchematic crystal structure of YbPtSb.