Andrey Zheludev: Pressure-induced criticality in organic quantum paramagnets

A variety of quantum antiferromagnets have a spin-singlet ground state and a gap in the magnetic excitation spectrum. For over a decade these systems have been employed as prototypes for the study of field-induced quantum phase transitions. The latter are in the XY universality class, have a dynamic critical exponent z=2, and can be viewed as a Bose-Einstein condensation of magnons.

Much less studied and potentially more interesting are quantum phase transitions in gapped spin systems occurring in zero field. In practice, the only feasible way to tweak exchange parameters in real materials is by applying mechanical pressure or stress. To date, the only known example of a pressure-induced transition is that in the spin dimer system TlCuCl3. New opportunities opened up when the search was extended to organic materials that are typically soft compounds, particularly susceptible to pressure.