Observing a supersolid—a state of matter that has both superfluid and solid properties—has been a challenge for decades. The constituent particles of a supersolid form a rigid, ordered structure but can also flow without dissipating energy. This paradoxical behavior was observed in cold-atom experiments only in the last five years [1–5]. Researchers typically make cold-atom supersolids starting from superfluid phases, leaving open the question of how supersolidity appears from other phases. Now, a team led by Francesca Ferlaino at the University of Innsbruck, Austria, has shown that when starting from a thermal gas, a supersolid’s crystalline and superfluid orders arrive and decay sequentually at the birth and death of a supersolid [6]. The results suggest that temperature plays a definitive role in the appearance of supersolidity.
The existence of a supersolid state was first proposed in 1957, long before experimentalists knew how to achieve it [7]. The first experiments focused on realizing supersolidity in helium, with researchers trying to move a helium sample from a solid, crystalline state to a supersolid one. Lacking unambiguous success, researchers started looking for alternative systems to obtain a supersolid [8].
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