QFS2016 Book of Abstracts

Abstracts

P4.20 Momentum distribution of liquid 4 He across the normal-superfluid transition Guillem Ferr´e, Jordi Boronat Universitat Polit`ecnica de Catalunya Departament de F´ısica Barcelona Quantum Monte Carlo group Calle Jordi Girona, 1-3, 08034 Barcelona, Spain We have carried out a study of the momentum distribution of liquid 4 He across the normal-superfluid transition temperature using the path integral Monte Carlo method. The momentum distribution and one-body density function have been accurately calculated in a range of temperatures which crosses the critical point. Our results show that a kink in the momentum distribution is present only in the superfluid region and disappears when crossing the transition temperature, in a behavior currently unexplained by theory. This kink appears in the range of momentum corresponding to the roton excitation , whose dynamic structure factor peak amplitude is already known to drop when the fluid becomes normal. P4.21 Measurements of ion motion and trapping in solid helium using a planar injector M. J. Fear(1), A. A. Levchenko(2), Yu. V. Kotov(2), P. M. Walmsley(1), A. I. Golov(1) 1) School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK 2) Institute of Solid State Physics, RAS, Chernogolovka, Moscow Region 142432, Russia A novel type of planar ion injector, with carbon nanotubes embedded into a conducting surface, is constructed. When in contact with solid helium, depending on the polarity of electric field at the surface, either positive or negative ions can be injected. We studied the motion of ions in a single crystal of hcp 4 He, grown inside a diode, one plate of which had such an injector. Step-like and pulsed injection of ions of both signs were employed. The measured time-dependent records of current, arriving at the second electrode, allowed to quantify the temperature dependences of ion mobilities, rates of trapping by dislocations and lifetimes of trapped states.

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