Helium atoms were believed to be strongly bound within the interstitial channels in bundles of C nanotubes. In a recent paper (Ancilotto et al., 2004) inhomogeneity in the size distribution of nanotube radii was shown to make a system of 4He atoms in such an environment effectively a four-dimensional Bose gas, thus permitting a Bose-Einstein condensation of the adsorbed atoms into the minimum energy state. This surprising result was obtained for a model of non-interacting atoms in a continuum distribution of (virtually) infinite interstitial channels. Here an investigation was made of how the singular thermal properties of the ideal system and the occurrence of Bose-Einstein condensation were affected by a more realistic modeling of a bundle of nanotubes where (i) the number of nanotubes was finite and where (ii) 4He atoms adsorbed within the same interstitial channel interact among themselves. Also in this case an anomalous heat capacity close to the ideal condensation temperature was observed; thus suggesting the persistence of the condensation transition for interacting 4He atoms, which might be experimentally observably.

Condensation of Helium in Interstitial Sites of Carbon Nanotubes Bundles. B.Marcone, E.Orlandini, F.Toigo, F.Ancilotto: Physical Review B, 2006, 74[8], 085415 (5pp)