QFS2016 Book of Abstracts

Abstracts

P4.16 Head-on collision of xenon atoms against superfluid 4-helium droplets. Coppens Fran¸cois, Leal Antonio, Barranco Manuel, Halberstadt Nadine, Pi Mart´ı 1)Universit´e Paul Sabatier, Physics, LCAR/IRSAMC, 118 route de Narbonne, 31062 Toulouse 2)Universitat de Barcelona, Facultat de F´ısica, Departament FQA, Diagonal 645, 08028 Barcelona We study the head-on collision of a heliophilic xenon atom with a superfluid helium droplet made of 1000 atoms. At variance with previous findings for a heliophobic cesium atom of similar atomic weight, it is found that the xenon atom has to hit the droplet with a large kinetic energy to get across it without being captured. When this happens the xenon impurity does not emerge as a bare atom; instead, due to its heliophilic character, it carries away some helium atoms whose number depends on the collision energy. 1) Department of Physics, University of Vermont, Burlington, VT 05405, USA 2) Institut f¨ur Theoretische Physik, Universit¨at Leipzig, D-04103, Leipzig, Germany Pressure driven flow of a superfluid inside a narrow channel can be maintained by the nucleation of vortices and their resulting motion across the flow lines. The maximum velocity of the superfluid is set by a nucleation rate which crucially depends on the microscopic details of the vortex cores and flow profile. Within the kinetic vortex theory, we have determined the critical superfluid velocity inside mesoscale constrictions and obtain agreement with experimental results for superfluid helium-4 in nanopores. In the small pore limit, when the ratio of pore radius to correlation length is of order unity, we find a drastic suppression of the superfluid velocity due to a reduction in the energy barrier of flow reducing excitations. P4.17 Dissipative superfluidity and mesoscale confinement Adrian Del Maestro(1) and Bernd Rosenow(2)

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