Giant thermopower in carbon nanotubes: A one-dimensional Kondo system

The electrical transport properties of single-wall carbon nanotubes are shown to be strongly influenced by the presence of transition-metal impurities derived from the catalyst introduced to stimulate their growth. Data on thermoelectric power and electrical resistance in the temperature range 10–400 K were obtained on a series of samples prepared using $M-Y$ catalysts $(M=\mathrm{Cr},$ Mn, Co, Fe, Ni). The unusual transport behavior observed is tentatively assigned to an interaction between the magnetic moment of the M atom and the spin of the conduction π electrons of the nanotubes, i.e., the Kondo effect.