Magnetotransport in iodine-doped single-walled carbon nanotubes

Abstract

Magnetoresistance (MR) and magnetothermoelectric power (MTEP) of iodine-doped single-walled carbon nanotubes (I@SWNT) under magnetic fields up to 14 T are investigated from room temperature (300 K) down to 1.6 K. Our results on resistivity and thermoelectricpower (TEP) in a zero magnetic field are similar to those reported by Grigorian et al. [Phys. Rev. Lett. 80, 5560 (1998)] The positive sign of the TEP values indicates that the majority of the carriers in the I@SWNT are holes. The broad enhancement of TEP at temperatures of 30\char21{}200 K shows quasilinear temperature dependence and is consistent with sharply varying density of states near the Fermi level with additional contribution from the spin-orbit scattering in the normal metallic characteristics of the I@SWNT. For $Tl7\text{ }\text{K}$, MR is negative and it decreases with ${H}^{2}$ followed by the ${H}^{1/2}$ dependence at around $H=2\text{ }\text{T}$ which is characteristic for the weak localization. In the range $7\text{ }\text{K}lTl70\text{ }\text{K}$, MR is positive at low magnetic field and becomes negative at higher magnetic field. The negative MR in the high magnetic fields decreases linearly. At $T\ensuremath{\ge}\ensuremath{\sim}100\text{ }\text{K}$, MR is positive up to 14 T, which could be the result of spin-orbit scattering in the I@SWNT. The MTEP decreases under magnetic field at $Tl90\text{ }\text{K}$. The reduction in MTEP is originated from the delocalization of electron wave functions under the magnetic field. At $Tg90\text{ }\text{K}$, the thermal fluctuation dominates the effect of magnetic fields resulting the MTEP to be the same as the zero magnetic field TEP.