We show that the intercalating of alkali atoms with adequate concentration can transform a metallic single-walled carbon nanotube (SWCNT) into a semiconductor tube or a semiconductor SWCNT into a semiconductor tube with different band gaps due to a unique feature of the band structures in some SWCNTs as quasi-one-dimensional materials. As examples, we predict the intercalated structure ${\mathrm{Li}}_2{\mathrm{C}}_{60}$ in the (5,0) tube to be a semiconductor while the pure (5,0) tube is a metal and the structure ${\mathrm{Li}}_2{\mathrm{C}}_{112}$ in the (4,2) tube to be a semiconductor with a direct gap while the pure (4,2) tube has an indirect gap. Results of other alkali atoms intercalating in various carbon nanotubes show that this transition mechanism is quite general.

• Received 13 January 2005

DOI:https://doi.org/10.1103/PhysRevB.71.165438