One-Dimensional Phonon State of 4He Films Adsorbed in Straight Nanopores |
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Authors: | Yuki Matsushita Junko Taniguchi Ryo Toda Hiroki Ikegami Taku Matsushita Mitsunori Hieda Nobuo Wada |
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Affiliation: | (1) Department of Physics, Nagoya University, Nagoya 464-8602, Japan;(2) Department of Applied Physics and Chemistry, University of Electro-Communications, Chofu 182-8585, Japan;(3) Low Temperature Physics Laboratory, RIKEN, Wako 351-0198, Japan |
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Abstract: | We have studied heat capacities of 4He adsorbed in straight nanopores 1.8, 2.2, and 2.8 nm in diameter. Heat capacities of the 4He fluid film on the solid layer at 0.08–0.4 K show power laws close to T in 1.8 nm pores, close to T
2 in 2.8 nm pores, and a crossover from T to T
2 with increasing temperature in 2.2 nm pores. These heat capacities are explained by a model assuming a phonon dispersion
with continuous one-dimensional (1D) states in the axial direction and discrete energy levels in the azimuthal direction.
By fitting experimental data to the model, the phonon velocity along the pore axis and the energy gap for propagation in the
cross section are derived. At temperatures sufficiently lower than the energy gap, where the thermal wave length of phonons
is much longer than the effective pore diameter, the 4He fluid films show a T-linear heat capacity of 1D phonons propagating only along the pore axis. At higher temperatures, a 1D-2D crossover of phonons
occurs.
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Keywords: | Low-dimensional quantum fluid Helium 4 Phonon Bose-Einstein statistics Nanopores |
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