Evidence of superfluidity in a dipolar supersolid from nonclassical rotational inertia

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Science  12 Mar 2021:
Vol. 371, Issue 6534, pp. 1162-1165
DOI: 10.1126/science.aba4309

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A supersolid rotation

When a bucket of water is rotated, the water rotates with the vessel, contributing to the total moment of inertia. If such an experiment were done with a superfluid, it would decouple from the vessel and would not contribute to rotation. Tanzi et al. studied an intermediate case, a supersolid, which is predicted to only partially decouple, resulting in a moment of inertia smaller than the classical value. Whereas previous such experiments were done with helium, the authors used a gas of highly magnetic dysprosium atoms in an optical trapping potential that was suddenly changed, causing the gas to oscillate. Measuring the frequency of these oscillations provides evidence for a reduced moment of inertia.

Science, this issue p. 1162


A key manifestation of superfluidity in liquids and gases is a reduction of the moment of inertia under slow rotations. Nonclassical rotational effects have also been considered in the context of the elusive supersolid phase of matter, in which superfluidity coexists with a lattice structure. Here, we show that the recently discovered supersolid phase in dipolar quantum gases features a reduced moment of inertia. Using a dipolar gas of dysprosium atoms, we studied a peculiar rotational oscillation mode in a harmonic potential, the scissors mode, previously investigated in ordinary superfluids. From the measured moment of inertia, we deduced a superfluid fraction that is different from zero and of order of unity, providing direct evidence of the superfluid nature of the dipolar supersolid.

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