This Swiss-Korean collaboration exploits molecular crystals of organic and meatal-organic origin to further understanding of emerging states in quantum spin systems.

Lay summary

A quantum critical point is a zero-temperature singularity in phase diagram of quantum matter originating from intense quantum fluctuations, and is a central theme in current condensed-matter research. One surprising aspect regarding a quantum critical point is that strong quantum critical fluctuations actually persist up to relatively high temperatures leading to universal behaviour in physical observables. Establishing universality classes of a variety of quantum phase transitions is of fundamental importance recalling that a similar task for classical thermal transitions marks one of the triumphs in the history of modern physics. Another highly attractive, and potentially practical, aspect is that a quantum critical point is considered a probable source of novel phases such as strange metal or unconventional superconducting ones. These aspects naturally motivates one to dream of experimental classification of various quantum critical points and their critical behaviour, and to apply those insights for discovering exotic quantum phases of novel properties or functionalities. Here we tackle this challenging task by harnessing molecular crystals, metal-organic compounds and organic insulators, for quantum magnets which are represented by the interacting spins localized on a lattice. A compelling aspect of quantum magnets for studying quantum criticality is that a simple and well-defined Hamiltonian, without complication from itinerant electrons or charge fluctuations, allows close comparison between experiments and theories.