Is quantum criticality always avoided? The case of a tricritical point

In families of quantum materials such as the cuprates, Fe-based superconductors, and heavy-fermion systems, there is a second-order transition to a magnetic state that can be driven towards low temperatures by non-thermal tuning parameters (chemical doping, pressure). The quantum critical point, however, is masked or suppressed by the emergence of new properties like unconventional superconductivity or by a change in the nature of the phase transition. These phenomena originate from magnetic fluctuations which are enhanced by the proximity to the avoided quantum critical point. In this presentation, I will show that the ubiquitous avoidance of quantum criticality seems to apply to another type of quantum critical point, the quantum tricritical point, where two types of distinct fluctuations are enhanced simultaneously. Using chemical substitution, we drive LaCrSb₃ towards a quantum tricritical point. The phase diagram showcases the avoidance of quantum criticality, with a new phase appearing above the putative quantum tricritical point.

Funding from UC Laboratory Fees Research Program (LFR-20-653926). This research used resources at the HFIR, a DOE Office of Science User Facility operated by the ORNL.