Fig. 4

Phase transition in the quantum limit of TaAs. a Resistivity for \({\mathbf{J}} \bot ({\mathbf{B}}||{\mathbf{c}})\), showing a kink near 80 T at low temperature. b The ultrasonic attenuation at 315 MHz for \({\mathbf{k}}||{\mathbf{B}}||{\mathbf{c}}\), where k is the propagation wavevector of the longitudinal (compressional) sound, and with data from 0 to 65 T shown in the inset. c Change in the speed of sound for the same configuration as the attenuation shown in (b). Data from two different experiments—one from 0 to 65  T and one from 45 to 95 T—are combined in this plot. Above 2.5 K the sound velocity flattens out above 80 T  and the attenuation is only weakly field dependent. Below 2.5 K, however, both the sound velocity and the ultrasonic attenuation increase rapidly with field. The red line is an interpolation of the data, highlighting the abruptness of the transition as a function of temperature