Quantum phenomena in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with 3He. A giant isotope effect

Abstract

The coefficient of radial thermal expansion αr of bundles of single-walled carbon nanotubes saturated with 3He up to a molar concentration of 9.4% has been studied over temperatures of 2.1–9.5 K by high-sensitivity capacitance dilatometry. In the interval 2.1–7 K a negative αr was observed, with a magnitude exceeding the largest negative values for pure and 4He-saturated nanotubes by three and two orders of magnitude, respectively. The contributions of the two He isotope impurities to the negative thermal expansion of the nanotube bundles are most likely related to spatial redistribution of 4He and 3He atoms by tunneling at the surface of and inside nanotube bundles. The isotope effect turned out to be huge, probably owing to a higher tunneling probability for 3He atoms.