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

TL;DR

This study reveals a giant isotope effect in the negative radial thermal expansion of single-walled carbon nanotube bundles doped with 3He, attributed to quantum tunneling differences between isotopes.

Contribution

It demonstrates a significantly enhanced negative thermal expansion in nanotubes doped with 3He, highlighting quantum tunneling as a key factor, which was not previously observed.

Findings

Negative thermal expansion exceeds that of pure and 4He-doped nanotubes

Giant isotope effect observed due to tunneling differences

3He doping causes a three to two orders of magnitude increase in negative expansion

Abstract

The radial thermal expansion {\alpha}r of bundles of single-walled carbon nanotubes saturated with 3He up to the molar concentration 9.4% has been investigated in the temperature interval 2.1-9.5 K by high-sensitivity capacitance dilatometry. In the interval 2.1-7 K a negative {\alpha}r was observed, with a magnitude which exceeded the largest negative {\alpha}r values of 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 connected with the spatial redistribution of 4He and 3He atoms by tunneling at the surface and inside nanotube bundles. The isotope effect turned out to be huge, probably owing to the higher tunneling probability of 3He atoms.