The quantum-mechanical orbitals in carbon nanotubes are doubly degenerate over a large number of states in the Coulomb blockade regime. We argue that this experimental observation indicates that electrons are reflected without mode mixing at the nanotube-metal contacts. Two electrons occupying a pair of degenerate orbitals (a ``shell'') are found to form a triplet state starting from zero magnetic field. Finally, we observe unexpected low-energy excitations at complete filling of a four-electron shell.
@article{arxiv.cond-mat/0508401,
title = {Persistent Orbital Degeneracy in Carbon Nanotubes},
author = {A. Makarovski and L. An and J. Liu and G. Finkelstein},
journal= {arXiv preprint arXiv:cond-mat/0508401},
year = {2009}
}