Possible explanation for the conductance of a single quantum unit in metallic carbon nanotubes

The quantum conductance of a metallic carbon nanotube with one end immersed in a jellium metal is studied. We find that the incident π*-band electrons, having a very high angular momentum with respect to the tube axis, go through the tube without being scattered by the free electrons in surrounding metal and contribute a quantum unit (2e²/h) to the conductance. On the other hand, the incident π-band electrons, with the p_z atomic orbitals in phase along the tube circumference, experience strong resonant back-scattering because the low-angular-momentum states at the Fermi level have a dominantly metallic character in the nanotube-jellium metal coexistence region. These results provide a possible explanation for the experimentally observed conductance of one quantum unit instead of two for nanotubes with one end dipped into liquid metal such as mercury.