Universal interaction-driven gap in metallic carbon nanotubes

Clean experimental testing grounds for strongly interacting electrons confined to one dimension are hard to find. Thus, suspended carbon nanotubes (CNTs) are a unique model system. Previous work showed that electron transport in suspended metallic CNTs can be frozen by strong electron-electron interactions. However, a detailed understanding of this exotic insulating phase has remained elusive. Here, the authors characterize the energy gap associated with the insulating phase in nominally metallic CNTs, and compare the gap to precise measurements of CNT diameter and chirality.