Magnetotransport in transparent single-wall carbon nanotube networks

An experimental study of the low temperature magnetotransport in optically transparent single-wall carbon nanotube (SWNT) networks is reported. The SWNT network shows Coulomb gap variable-range hopping conduction at low temperatures. The magnetoresistance (MR) involves the interplay of two phenomena: a forward interference process leading to negative MR together with shrinkage of electronic wave function contributing to the positive MR. These two mechanisms fit the low-field data. The analysis of magnetotransport data gives an estimate for intrinsic parameters including localization length and Coulomb gap. The temperature dependence of the forward interference mechanism is shown to follow an inverse power-law dependence with an exponent close to 1, indicating the weak scattering process involved in the transport.

Figure 1

SEM image of the transparent SWNT network (the scale bar is $1\mu \mathrm{m}$).

Figure 2

(a) Temperature dependence of the zero-field resistance. Inset: Reduced activation energy $W$ vs $T$. (b) $\ln R$ vs $T^{-p}$ plot showing the linear relationship (arrows indicate limit of linear regime fit).

Figure 3

(a) Transverse field dependence of MR at various temperatures. The solid line is the wave-function shrinkage fit to low-field $(B<4\mathrm{T})$ positive MR at $1.3\mathrm{K}$. (b) Low-field MR at various temperatures. The solid lines are fits to Eq. (3) described in text. (c) Coefficient of term linear in field $\left(a_1\right)$ vs $T$.

Figure 4

(a) Field dependence of MR for transverse (open symbols) and longitudinal fields (filled symbols) at $4.2\mathrm{K}$ (triangles) and $10\mathrm{K}$ (squares). (b) Field dependence of MR for transverse (open symbols) and longitudinal fields (filled symbols) at $1.3\mathrm{K}$. (Solid curves are a guide to the eye.)