Gate-Dependent Magnetoresistance Phenomena in Carbon Nanotubes

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under a magnetic field as large as 50 T. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidence for unconventional magnetoresistance is presented and interpreted by means of theoretical calculations.

Figure 1

Differential conductance vs applied bias voltage at 4 K for $V_G=0\mathrm{V}$. The arrow indicates the high energy regime studied under 50 T at 4 K. In the inset, the gate voltage effects on the differential conductance for $V_b=20\mathrm{m}\mathrm{V}$ at 80 K.

Figure 2

Magnetoconductance $\Delta G(B)$ up to 50 T for $B_{\parallel }$ and $B_{\perp }$ with a bias voltage $V_b=300\mathrm{m}\mathrm{V}$ and zero gate voltage at 80 K. Solid lines represent the quasi-2D WL fits for both configurations. Inset: the predicted $\Delta G(B_{\parallel })$ from Eq. (1) in a very high field, superimposed to our measurement.

Figure 3

Left panel: Magnetoconductance $\Delta G(B_{\parallel })$ up to 50 T with a bias voltage $V_b=50\mathrm{m}\mathrm{V}$ and for $V_G=0$ and 10 V at 4 K. Inset: low magnetic-field fit with the quasi 2D WL model (solid line), using Eq. (1) up to $B_{\parallel }=3\mathrm{T}$. Right panel: The low field variations of $\Delta G(B_{\parallel })$ for different gate voltages from 0 to 10 V.

Figure 4

Conductance versus Fermi level position, for a disordered $(22,22)$ nanotube, and two values of the parallel magnetic field: $B_{\parallel }=0\mathrm{T}$ (solid line) and $B_{\parallel }=50\mathrm{T}$ (dashed line). Two disorder strengths are considered: $W/{\gamma }_0=1$ (upper panel) and $W/{\gamma }_0=2$ (lower panel). In the strong disorder case, the two arrows indicate possible Fermi level positions for $V_G=0\mathrm{V}$ (left) and $V_G=10\mathrm{V}$ (right).