Anomalous low temperature specific heat of ³He inside nanotube bundles

Helium atoms and hydrogen molecules can be strongly bound inside interstitial channels within bundles of carbon nanotubes. An exploration of the low energy and low temperature properties of ³He atoms is presented here. Recent study of the analogous ⁴He system has shown that the effect of heterogeneity is to yield a density of states N (E) that is qualitatively different from the one-dimensional (1D) form of N(E) that would occur for an ideal set of identical channels. In particular, the functional form of N(E) is that of a 4D gas near the very lowest energies and a 2D gas at somewhat higher energies. Similar behavior is found here for ³He. The resulting thermodynamic behavior of this fermi system is computed, yielding an anomalous from of the heat capacity and its dependence on coverage.