Defects, quasibound states, and quantum conductance in metallic carbon nanotubes

The effects of impurities and local structural defects on the conductance o f metallic carbon nanotubes are calculated using an nb initio pseudopotenti al method within the Landauer formalism. Substitutionally doped boron or ni trogen produces quasibound impurity states of a definite parity and reduces the conductance by a quantum unit (2e(2)/h) via resonant backscattering. T hese resonant states show strong similarity to acceptor or donor states in semiconductors. The Stone-Wales defect also produces quasibound states and exhibits quantized conductance reduction. In the case of a vacancy, the con ductance shows a much mon complex behavior than the prediction from the wid ely used pi-electron tight-binding model.