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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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