A specific quantum magnet actually turns from a solid into a liquid as you cool it down toward absolute zero.
Almost everything in the universe freezes when it gets cold and melts when it gets hot. The material erbium heptatantalate breaks this rule by developing a solid-like magnetic order and then melting back into a liquid-like state as the temperature drops further. This inverse melting happens because of the weird way quantum fluctuations compete with the material's internal structure. It is a rare state of matter where the normal laws of thermodynamics seem to run in reverse. Studying this could lead to new ways of manipulating magnetic data using only temperature changes. It provides a unique window into the strange stability of quantum systems.
Melting upon cooling in a quantum magnet
arXiv · 2605.04611
Heating enhances thermal fluctuations and typically leads to melting of solids, but in exceptional cases, heating can also cause liquids to solidify. The paradigm of this counterintuitive phenomenon is solidification of liquid $^3$He upon increasing temperature, known as the Pomeranchuk effect. Here we show that such inverse melting also appears in quantum magnetism. We find that, on cooling, the Ising-like triangular-lattice antiferromagnet erbium heptatantalate first develops a three-sublattic