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.
16