Nature Materials 1, 190–194 (2002).

In this article, the manufacture of SWNTs was incorrectly described in lines 18 and 19 of the second column on page 191. It should have read as follows:

The SWNTs were manufactured by laser vaporization of carbon rods, which were doped with Co/Ni in a 1:1 ratio in an atmosphere of Ar.

An additional statement should also have appeared in the Acknowledgements section as follows:

The SWNTs used in this work were supplied by M. Kappes and F. Hennrich (University of Karlsruhe, Germany).