QFS 2016 Book of Abstracts

Abstracts

O1.3 Gap-induced Elasticity of Atomically Thin 4 He Films Shirahama Keiya(1), Takahashi Daisuke(2),

Kogure Takayuki(1),

Yoshimura Hitomi(1), Higashino Rama(1) (1) Keio University, Department of Physics, Yokohama 223-8522, Japan (2) Ashikaga Institute of Technology, Division of General Education, Ashikaga 326-8558, Japan 4 He films undergo a quantum phase transition from localized to superfluid states by increasing coverage n. We made torsional oscillator (TO) studies for films adsorbed on nanoporous glasses. A TO with localized films showed an apparent supersolid behavior, an increase in frequency f with a peak in Q-1. FEM analyses reveal that the behavior results from the stiffening of He films at low T. Q-1 and f are fitted well to a Debye-like activation with a distributed energy gap: The film elasticity is governed by gap between the localized and extended states, which decreases to zero as n approaches the critical coverage nc, and excitation over the gap. The elastic constant K − 1 = n 2 dG/dn that is estimated assuming that the He chemical potential G is at the middle of the gap agrees with K − 1 obtained from FEM within an order of magnitude. O1.4 Third sound propagation with 4 He films adsorbed on 10 nm multiwall carbon nanotubes Emin Menachekanian, Vito Iaia, Mingyu Fan, Chaowei Hu, Ved Mittal, Raul Reyes, Wenxin Xie, and Gary A. Williams University of California, Los Angeles, CA 90095, USA Third sound propagation is studied for 4 He films adsorbed on multiwall carbon nanotubes with diameters of 10 ± 1 nm . Strong layering effects are seen for film thicknesses between 3 and 6 atomic layers. Temperature sweeps at fixed thickness show a strong broadening of the KT transition and high attenuation at the onset, and results will be compared with the theory of Guyer and Machta for the KT transition on a cylinder.

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