  We investigate transport through a single impurity in metallic zigzag carbon
nanotube and find the conductance sensitively depends on the impurity strength
and the bias voltage. It is rather interesting that interplay between the
current-carrying scattering state and evanescent modes leads to rich phenomena
including resonant backward scattering, perfect tunneling and charge
accumulations. In addition, we also find a dual relation between the
backscattered conductance and the charge accumulation. At the end, relevance to
the experiments is discussed.
