Disorder effect on electronic and optical properties of doped carbon nanotubes

In this work, we investigate the effects of disorder in the doped carbon nanotubes. Based on the extended Su-Schrieffer-Heeger model, it is shown that with the increase of doped impurity atoms, such as nitrogen or boron, the symmetry of the hopping processes among the doped and carbon lattices collapses, and the statistics of the nearest neighbor energy level spacing changes from the Poisson distribution to the Wigner distribution, indicating the occurrence of disorder effect in heavily doped nanotubes. As a result, the nanotube changes from a metal to a semiconductor. We also study the disorder effect on linear optical absorption in doped nanotubes. It is demonstrated that the linear optical absorption can be greatly suppressed due to the collapse of the discrete spatial symmetry in heavily doped nanotubes. Based on the random matrix theory, we carry out a theoretical analysis, which agrees well with our numerical simulations.