  The level spectrum of a single-walled carbon nanotube rope, studied by
transport spectroscopy, shows Zeeman splitting in a magnetic field parallel to
the tube axis. The pattern of splittings implies that the spin of the ground
state alternates by 1/2 as consecutive electrons are added. Other aspects of
the Coulomb blockade characteristics, including the current-voltage traces and
peak heights, also show corresponding even-odd effects.
