Oscillating chiral currents in nanotubes: A route to nanoscale magnetic test tubes

With a view to optimizing the design of carbon-nanotube (CNT) windmills and to maximizing the internal magnetic field generated by chiral currents, we present analytical results for the group-velocity components of an electron flux through chiral carbon nanotubes. Chiral currents are shown to exhibit a rich behavior and can even change sign and oscillate as the energy of the electrons is increased. We find that the transverse velocity and associated angular momentum of electrons are a maximum for nonmetallic CNTs with a chiral angle of $18°$. Such CNTs are therefore the optimal choice for CNT windmills and also generate the largest internal magnetic field for a given longitudinal current. For a longitudinal current of order ${10}^{-4}\text{A}$, this field can be of order ${10}^{-1}\text{T}$, which is sufficient to produce interesting spintronic effects and a significant contribution to the self-inductance.

Figure 1

(Color online) Velocity components for the $\left(8,m\right)$ family of CNTs plotted against the energy $E$ (eV), where $m=8,4,5,6$ in (a)–(d), respectively. The red curves show the transverse velocities $v_x\left[q,k_y^{+}\left(q,E\right)\right]/v_F$ of right-moving electrons belonging to individual channels $q$. The black curves show the total velocity $v_x^{\left(n,m\right)}\left(E\right)$ of Eq. (3).