Cooling a Thermal Cloud to a Supersolid

O bserving 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