Most materials go from being solids to liquids when they are heated. One rare counter-example is helium-3, which can solidify upon heating. This counterintuitive and exotic effect, known as the Pomeranchuk effect, may now have found its electronic analog in a material known as magic-angle graphene, says a team of researchers from the Weizmann Institute of Science led by Prof. Shahal Ilani, in collaboration with Prof. Pablo Jarillo-Herrero's group at the Massachusetts Institute of Technology (MIT).

This result, published today in Nature, comes thanks to the first ever measurement of electronic entropy in an atomically-thin two dimensional material. "Entropy describes the level of disorder in a material and determines which of its phases is stable at different temperatures," explains Ilani. "Our team set up to measure the electronic entropy in magic angle graphene to resolve some of its outstanding mysteries, but discovered another surprise."

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