Ultra-low-temperature phase diagram near the quantum critical point in the model nematic insulator TmVO₄

Ferroquadrupole order of local atomic states provides a realization of electronic nematic order. Here, we examine the phase diagram of a representative model nematic system, TmVO₄, for which magnetic field acts as a transverse effective field for the quadrupole order, driving the system through a quantum phase transition. We study the material using AC magnetic susceptibility, tracing the phase boundary from the zero-field value of 2.15 K down to 5 mK at a field of approximately 5200 Oe, revealing the profound effect of hyperfine interactions in the phase diagram. Measurements were performed at the High B/T Facility of the National High Magnetic Field Laboratory. Surprisingly, a semiclassical, single ion, mean field treatment appears to sufficiently capture the shape of the phase boundary down to the lowest temperatures measured, indicating that the ground state is characterized by coupled lattice-electronic-nuclear fluctuations.