Mesoscopic transport through toroidal carbon nanotubes threaded with a THz magnetic flux

We have investigated the quantum transport through mesoscopic systems with a toroidal carbon nanotube coupled with two metal leads (N-TCN-N) threaded with an ac magnetic flux. The energy shifting takes place by applying the magnetic flux, and this shifting arises from both the dc and ac components of magnetic flux. The dc magnetic flux $\phi$ induces the periodic variation of energy gap E g of the TCN, and the ac magnetic flux component always increases the energy gap. As the photon energy is larger than the energy gap $\hbar\omega > E_g$ , the electrons in the valence band can jump to the conductance band at zero temperature, and the tunneling current appears for $eV > E_g/2 + n\hbar\omega$ , ( $n=0,\pm 1,\pm 2...$ ). The differential conductance and tunneling current display clear effect of ac flux by modifying the current oscillation structures. The photon-assisted tunneling current exhibits stair-like I-V characteristics, and it shows different behaviors for different TCN systems. The magnitude of the current is suppressed by the applied ac flux. We also present the time-dependent current evolution, which is contributed by the oscillating current components. Copyright Springer-Verlag Berlin/Heidelberg 2004