Evidence of 1D behavior of He4 confined within carbon-nanotube bundles -: art. no. 025901

We present the first low-temperature thermodynamic investigation of the controlled physisorption of He-4 gas in carbon single-wall nanotube (SWNT) samples. The vibrational specific heat measured between 100 mK and 6 K demonstrates an extreme sensitivity to outgassing conditions. For bundles with a few number of nanotubes the extra contribution to the specific heat, C-ads, originating from adsorbed He-4 at very low density displays 1D behavior, typical for He atoms localized within linear channels as grooves and interstitials, for the first time evidenced. For larger bundles, C-ads recovers the 2D behavior akin to the case of He-4 films on planar substrates (grafoil).