High Field Ultrasound Measurements in UPt3 and the Single Energy Scale Model of Metamagnetism

We report longitudinal ultrasound velocity measurements for magnetic fields up to 33 T applied parallel to the a-axis of the heavy electron compound UPt$_{3}$. A characteristic dip in the sound velocity at the metamagnetic critical field, $H_{c}=20$ T, reported in earlier work is reproduced and shown to be independent of temperature at very low temperatures. We show that the single energy scale model (B.S. Shivaram et al., Phys. Rev. B89, 241107(R), 2014) captures the observed key features of the field dependence in the sound velocity shift, $\delta v_{s}$. The shift $\delta v_{s}$ at $H_{c}$ is found to be inversely dependent on temperature above 3\thinspace K and assumes a fixed value at low T. This saturation in $\delta v_{s}$ below 3 K is accounted for by level broadening of the Uranium spin states.