Discovery of a spin supersolid and its giant magnetocaloric effect for extreme cooling

The extremely low-temperature refrigeration technology that can achieve a temperature below 1 K and provide stable cooling capacity is not only a frontier scientific topic but also a key expertise supporting the development of many fields. Recently, we have, for the first time, discovered a novel quantum state that combines the properties of both solids and superfluids, namely the spin supersolid, in the cobalt-based triangular lattice quantum magnetic material Na₂BaCo(PO₄)₂. Further studies show that this quantum state can lead to a giant magnetocaloric effect. Through the adiabatic demagnetization process, a low temperature of 94 mK has been successfully achieved, marking a breakthrough in low-temperature solid-state refrigeration without helium-3, and opening up a new pathway for extreme cooling using quantum materials. After a brief introduction to the supersolidity, this paper will elaborate on discovery of the spin supersolid and its giant magnetocaloric effect in a cobalt-based triangular lattice quantum material, as well as the realization of extremely-low temperature refrigeration. In combination with the recent progress on the topological excitation magnetocaloric effect found in Kitaev quantum spin liquids, this paper also looks ahead to the future prospects of solid-state refrigeration using quantum materials.