Chemical disorder strength in carbon nanotubes: Magnetic tuning of quantum transport regimes

We report on a theoretical study of quantum transport in carbon nanotubes in the presence of chemical-disorder-induced quasibound states, with a quantitative analysis of the relationship between the energy-dependent elastic mean free path and localization length. An external magnetic field applied perpendicularly to the nanotube axis is shown to induce a floating up in energy of the quasibound states, which results in giant magnetoconductance fluctuations under a Fermi level shift.

Figure 1

(Color online) Main frame: Length dependence of the Landauer conductance for the disordered (10,10) nitrogen-doped nanotube at several energies (doping is fixed to $0.1\%$). Inset: Conductance versus energy for the perfect (dashed line) and single-impurity (solid line) cases. Arrows show the considered energies for the scaling analysis (main frame).

Figure 2

Main frame: ${\ell }_e^K$ for several values of $n_{\mathrm{doping}}$ (from bottom to top curve, $0.3\%$, $0.2\%$, $0.1\%$, $0.05\%$). Inset (top): $\overline{T}$ at the CNP, for an average over $200$ configurations $(n_{\mathrm{doping}}=0.1\%)$. The linear fit (dashed) directly gives ${\ell }_e$. Inset (bottom): $\overline{\ln T}$ at $E=0.69\mathrm{eV}$, with linear fit (dashed) giving access to $\xi$ $(n_{\mathrm{doping}}=0.1\%)$.

Figure 3

Averaged conductance versus energy for a $(10,10)$ nanotube with a doping density of $n_{\mathrm{doping}}=0.1\%$, without magnetic field (left curve) and at $(r∕{\ell }_B{)}^2=1.2$ (right curve). The conductance is probed at various increasing lengths (from top to bottom, $L_{\mathrm{tube}}=200$ and $570\mathrm{nm}$). The dashed curve gives the single-impurity case.

Figure 4

Averaged magnetoconductance of a $(10,10)$ nanotube with a doping density of $n_{\mathrm{doping}}=0.1\%$, under a perpendicular magnetic field. Left curve: CNP. Right curve: $E=0.69\mathrm{eV}$. The dashed curves give the single-impurity case. The magnetoconductance is probed at various increasing lengths (from top to bottom, $L_{\mathrm{tube}}=50$, 150, $350\mathrm{nm}$).