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Second sound seen

A Publisher Correction to this article was published on 14 June 2021

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The two-fluid model of superfluids predicts a second, quantum mechanical form of sound. Ultracold atom experiments have now measured second sound in the unusual two-dimensional superfluid described by the Berezinskii–Kosterlitz–Thouless transition.

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Fig. 1: Universal jump in superfluid density.

Image courtesy of Panagiotis Christodoulou and Zoran Hadzibabic, University of Cambridge.

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Correspondence to Sandro Stringari.

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Stringari, S. Second sound seen. Nat. Phys. 17, 770–771 (2021).

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