Observation of dynamic atom-atom correlation in liquid helium in real space
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Liquid He-4 becomes superfluid and flows without resistance below temperature 2.17 K. Superfluidity has been a subject of intense studies and notable advances were made in elucidating the phenomenon by experiment and theory. Nevertheless, details of the microscopic state, including dynamic atom-atom correlations in the superfluid state, are not fully understood. Here using a technique of neutron dynamic pair-density function (DPDF) analysis we show that He-4 atoms in the Bose-Einstein condensate have environment significantly different from uncondensed atoms, with the interatomic distance larger than the average by about 10%, whereas the average structure changes little through the superfluid transition. DPDF peak not seen in the snap-shot pair-density function is found at 2.3 angstrom, and is interpreted in terms of atomic tunnelling. The real space picture of dynamic atom-atom correlations presented here reveal characteristics of atomic dynamics not recognized so far, compelling yet another look at the phenomenon.
CitationDmowski, W., Diallo, S., Lokshin, K., Ehlers, G., Ferré, G., Boronat, J., Egami, T. Observation of dynamic atom-atom correlation in liquid helium in real space. "Nature communications", 4 Maig 2017, vol. 8, núm. 15294, p. 1-6.