Helium in one-dimensional nanopores: Free dispersion, localization, and commensurate/incommensurate transitions with nonrigid orbitals

The single particle properties of helium in a carbon nanotube bundles can vary over an enormous range, from nearly free-particle dispersion in tube interiors and short-period interstitial channels to effective mass enhancement in longer-period channels. The competition between external potential and the He-He hard-core interaction caused an incommensurate-commensurate transition, where the doubly occupied domain-wall solitons mobility at high density exceeds the corresponding hole mobility below the transition.