S. Nakamura, K. Matsui, T. Matsui, Hiroshi Fukuyama
We report preliminary heat capacity and vapor pressure measurements of the first and second layers of helium-4 adsorbed on ZYX graphite. ZYX is known to have much better crystallinity than Grafoil, the most commonly-used exfoliated graphite substrate, such as a ten-times larger platelet size. This allows us to distinguish different phases in 2D 4He much more clearly and may provide qualitatively different insights into this system. We found a significantly asymmetric density-dependence of the heat-capacity peak associated with the 1/3 phase formation than that obtained with Grafoil. The 2nd-layer promotion density is determined as 11.78(7) nm-2 from the heat-capacity measurement of low density samples in the 2nd layer. The precise knowledge of this density is particularly important to establish the density scale in the second layer. The value is consistent with that deduced from our vapor pressure measurement. However, the chemical potential of the 1st layer of 4He obtained in the deduction process is consistently smaller than a theoretical calculation by 20 K.
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http://arxiv.org/abs/1207.3842
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