Elastic property of the Yb‐based heavy fermion compound YbPtSb

We report measurements of elastic constants detected close to a quantum critical point (QCP) of YbPtSb using one of the best‐established 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.Schematic crystal structure of YbPtSb.