Photon-assisted transport in a carbon nanotube calculated using Green’s function techniques

We investigate the quantum transport through a single-walled carbon nanotube connected to leads in the presence of an external radiation field. We analyze the conductance spectrum as a function of the frequency and strength of the field. We found that above a critical value of the field intensity, an enhancement of the conductance, or suppressed resistance, as a function of the field strength occurs. The conductance increases displaying oscillations which amplitude shows a strong dependence on the field frequency. For low radiation energies in comparison with the lead–carbon-nanotube coupling energies, the oscillations evolve toward a structure of well defined steps in the conductance. We have shown that in this range of frequencies, the field intensity dependence of the conductance can give direct information of single-walled carbon nanotube energy spectra.

Figure 1

(Color online) Schematized view of the CNT system considered.

Figure 2

Density of states for a (12,0) CNT under a radiation field of $h\nu =0.0005\gamma$ and different values of the field strength.

Figure 3

Density of states for (5,0) (upper panel) and (6,0) (lower panel) CNTs under a radiation-field strength of $V_0=0.3\gamma$ and different values of the field frequency.

Figure 4

(Color online) Normalized linear conductance of a (11,0) (upper panel) and a (12,0) (lower panel) CNT as a function of the oscillating field strength in unit of $\gamma$; solid black line corresponds to $h\nu =0.0005\gamma$, solid green (gray) line to $h\nu =0.005\gamma$, and blue (gray) dashed line to $h\nu =0.05\gamma$.

Figure 5

Normalized conductance of (12,0) (upper panel) and (11,0) (lower panel) CNTs as a function of the energy photon, in units of $\gamma$, for $V_0=0.3\gamma$, $V_0=0.45\gamma$, and $V_0=0.9\gamma$.

Figure 6

(Color online) Normalized conductance of a (15,0) CNT as a function of the oscillating field strength, in units of $\gamma$, for $h\nu =0.0005\gamma$. The corresponding DOS of the CNT is also plotted in the same energy range.

Figure 7

Normalized resistance for CNTs of different diameters as function of the oscillating field strength, (a) (9,0) CNT and (b) (18,0) CNT, for $h\nu =0.0005\gamma$.