Impurity driven inter-tube conductance in double-wall carbon nanotubes

Abstract The inter-tube conductance of double-wall carbon nanotubes with impurities is numerically studied. Same impurities lead to significantly different inter-tube conductance depending on the tube where they are located

Electronic states and quantum transport in double-wall carbon nanotubes

Electronic states and transport properties of double-wall carbon nanotubes without impurities are studied in a systematic manner. It is revealed that scattering in the bulk is negligible and the number of channels determines the average conductance. In the case of general incommensurate tubes, separation of degenerated energy levels due to intertube transfer is suppressed in the energy region higher than the Fermi energy but not in the energy region lower than that. Accordingly, in the former case, there are few effects of intertube transfer on the conductance, while in the latter case, separation of degenerated energy levels leads to large reduction of the conductance. It is also found that in some cases antiresonance with edge states in inner tubes causes an anomalous conductance quantization, $G=e^2/\pi\hbar$, near the Fermi energy.Comment: 24 pages, 13 figures, to be published in Physical Review

Magnetic-Field Dependence of Localization in Antidot Lattices

Localization length in antidot lattices in magnetic fields is numerically calculated based on a finite-size scaling method. The inverse localization length has a vanishingly small minimum at a magnetic field. This critical magnetic field corresponds to an insulator-quantum Hall transition. At around the critical field, the inverse localization length oscillates with a period of flux quantum Φ 0 = ch/e per passing through a unit cell. In hexagonal antidot lattices, a quantum oscillation of resistivity was observed in magnetic fields near or higher than an insulator-quantum Hall transition point. 1) The period is Φ 0 as a function of flux Φ passing through a unit cell where Φ 0 = ch/e is the aux quantum. The purpose of this paper is to study the localization length around an insulator-quantum Hall transition point in a hexagonal antidot lattice by a numerical finite-size scaling method. As a model of antidot lattice, we take a two-dimensional array of quantum-wire junctions, each of which is characterized by a scattering matrix calculated in a nearestneighbor tight-binding model. 2),3) We consider two kinds of disorders, i.e., the impurity potential and the fluctuation in the antidot diameter d. 4),5) We shall use a finite-size scaling method. 6),7) The inverse localization length α(L) is calculated for a long stripform antidot lattice with a finite width L. We assume a scaling hypothesis α(L)L = f (α 2D L) where α 2D is the inverse localization length in two dimension. The width of a strip system is chosen as L/ √ 3a = 8, 12, and 16 except at magnetic fields near a critical point, i.e., Φ/Φ 0 = 7. 75, 8, 8.25, 8.5, and 8.75 where calculations for the widest width of L/ √ 3a = 24 are performed. Scaling the calculated results of inverse localization length α(L), it is shown that the above finite-size scaling hypothesis works well. The present results are qualitatively in good agreement with those of experiments. 1) In the experiments, a prominent oscillation with a period Φ 0 appears in the magneticfield range near and higher than an insulator-quantum Hall transition. The critical magnetic field of the experiments, however, is Φ/Φ 0 ∼ 4 which is smaller than our result Φ/Φ 0 ∼ 8. This difference may be attributed to a difference in the value of d/a