Intrinsic Magnetoresistance of Single-Walled Carbon Nanotubes Probed by a Noncontact Method

The intrinsic magnetotransport effect of the single-walled carbon nanotube (SWNT) has been observed by the cavity perturbation technique, which is a noncontact method for evaluating transport properties. The inverse $Q$ factor of the cavity resonator, which corresponds to the resistance of the sample, shows a linear increase as a function of the magnetic field. The angular and tube diameter dependence of oriented SWNT thin films, and measurements using sorted SWNTs reveal that the observed positive magnetoresistance is due to the Aharonov-Bohm effect of metallic nanotubes.

Figure 1

(a) Schematic drawings of the SWNT and the typical energy dispersions of metallic and semiconducting SWNTs. (b) The predicted magnetic flux dependence of the energy gap [2]. The solid and broken lines are for metallic and semiconducting nanotubes, respectively. (c) The magnetic field dependence of the energy gap for metallic nanotubes with 1 and 3 nm diameters (thin and thick solid lines, respectively).

Figure 2

The magnetic field dependence of $\Delta f$ and $1/2\Delta Q$ of a highly oriented SWNT thin film at 4.2 K for $B\parallel \mathrm{\text{tube}}$ and $B\perp \mathrm{\text{tube}}$. Each value is normalized with the value at zero field. The diameter of the SWNTs used in the thin film is about 0.95 nm (grown by HiPco methods).

Figure 3

The typical magnetic field dependence of the $1/2\Delta Q$ at 4.2 K for oriented thin film with SWNTs grown by HiPco (circle) and supergrowth (square) methods. The diameter of the tubes is $0.95\pm 0.11\mathrm{nm}$ and 1–3 nm, respectively. Each value is normalized to the value for the zero field and its size factor $\gamma$. The raw HiPco data are taken from Fig. 2.

Figure 4

Comparison of the $1/2\Delta Q(B)-1/2\Delta Q(0)$ of oriented thin film with the mixed SWNTs (circle) and the semiconducting SWNTs (square) at 4.2 K.