Nonmagnetic impurity in carbon nanotubes with superconducting pair potentials

Effects of the superconducting pair potential on the impurity scattering processes in metallic carbon nanotubes are studied theoretically. The backward scatterings of electron- and hole-like quasiparticles disappear. The impurity gives rise to backward scatterings of holes for incident electrons, and it also induces backward scatterings of electrons for incident holes. Negative and positive currents induced by such scatterings between electrons and holes cancel each other. Therefore, the nonmagnetic impurity does not hinder the supercurrent in the regions where the superconducting proximity effects occur, and thus the metallic nanotube is a good conductor for Cooper pairs. Relations with experiments are discussed.