Anisotropic Condensation of Helium in Nanotube Bundles

TL;DR

This paper investigates the anisotropic condensation of helium atoms within carbon nanotube bundles, revealing a novel quasi-one-dimensional phase with unique thermodynamic properties and low binding energy.

Contribution

It introduces a new understanding of helium condensation in nanotube interstitial channels, including estimates of binding energy and critical temperature for this anisotropic phase.

Findings

Helium forms a low-energy, anisotropic condensed phase in nanotube bundles.

The specific heat of helium in this phase exceeds that of the host material at low temperatures.

The phase exhibits a remarkably low binding energy and critical temperature.

Abstract

Helium atoms are strongly attracted to the interstitial channels within a bundle of carbon nanotubes. The strong corrugation of the axial potential within a channel can produce a lattice gas system where the weak mutual attraction between atoms in neighboring channels of a bundle induces condensation into a remarkably anisotropic phase with very low binding energy. We estimate the binding energy and critical temperature for 4He in this novel quasi-one-dimensional condensed state. At low temperatures, the specific heat of the adsorbate phase (fewer than 2% of the total number of atoms) greatly exceeds that of the host material.