LAUSR

Much of what we know about quantum criticality comes from studies of quantum phase transitions between paramagnetic and magnetically ordered phases. These are usually driven by magnetic field or pressure. Here, the authors report that in CsFeCl${}_{3}$, one of the precious few materials exhibiting pressure-induced magnetic order, a similar transition can also be induced by chemical substitution. Cs${}_{1\ensuremath{-}x}$Rb${}_{x}$FeCl${}_{3}$ continuously evolves from a gapped quantum paramagnet to a critical gapless state and finally to magnetic long-range order. No bulky pressure cells are required, which makes all thermodynamic and spectroscopic properties easily accessible to measurement.