We have measured the differential conductance of individual multiwall carbon nanotubes. Coulomb blockade and energy level quantization are observed. The electron levels are nearly fourfold degenerate (including spin) and their evolution in magnetic field (Zeeman splitting) agrees with a $g$ factor of 2. In zero magnetic field the sequential filling of states evolves with spin $S$ according to $S=0\mathrm{}\to 1/2\to 0\dots$ . A Kondo enhancement of the conductance is observed when the number of electrons on the tube is odd.

• Received 14 August 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.156801