Aharonov-Bohm Conductance Modulation in Ballistic Carbon Nanotubes

We report on magnetoconductance experiments in ballistic multiwalled carbon nanotubes threaded by magnetic fields as large as 55 T. In the high temperature regime (100 K), giant modulations of the conductance, mediated by the Fermi level location, are unveiled. The experimental data are consistently analyzed in terms of the field-dependent density of states of the external shell that modulates the injection properties at the electrode-nanotube interface, and the resulting linear conductance. This is the first unambiguous experimental evidence of Aharonov-Bohm effect in clean multiwalled carbon nanotubes.

Figure 1

Left-hand panel: Magnetoconductance $G(V_g,B)$ at 100 K with magnetic field parallel to the tube axis. Selected gate voltages (in volts) are shown. Right-hand panel: 3D representation of $G(B,V_g)$ at 100 K.

Figure 2

(a) Theoretical magnetoconductance $G(\Delta E_f,\Phi )$ at 100 K for a $(72,72)$ diameter metallic nanotube in the flat band regime. The curves are calculated for different $\Delta E_F$ ranging from the CNP to slightly below the half value of the first vHS. (b) Comparison between the theoretical $G(\Phi )$ curves and the experimental ones under ${\tilde{V}}_g=0$, $-10$, $-16$, and $-20\mathrm{V}$. The fitting parameter $\Delta E_F$ is equal to 0, $-20$, $-42$, and $-46\mathrm{meV}$, respectively.

Figure 3

(a) Experimental magnetoconductance for selected ${\tilde{V}}_g$ values and their corresponding theoretical curves at 100 K (black dashed curves). The curves are shifted by $0.2G_0$ for clarity. (b) Sketch of the Schottky barrier at the contact with the parameters used in the model. (c) Corresponding Schottky barrier profiles at ${\Phi }_0/2$ for the different backgate voltages and based on parameters of Table . (d) 2D experimental graph of $G(V_g,\Phi )$ (left-hand graph) and the theoretical one based on Eq. (3) and Table  (right-hand graph).