Figure 1

(a) Resistivity of a suspended graphene sample ($S1$) versus carrier density induced by back gate (resistivity is displayed on a log scale). Inset: Atomic force microscope image of a typical suspended device. (b) Landau fan diagram $R_{xx}(V_g,B)$ at $T=7\mathrm{K}$ measured in sample $S3$. The dark blue lines indicate minima in $R_{xx}$. The dashed lines with integers indicate the corresponding filling factors.Reuse & Permissions

Figure 2

(a) $R_{xx}$ and $R_{xy}$ measured as a function of filling factor $\nu$ at $B=2\mathrm{T}$ and $T=1.7\mathrm{K}$ for sample $S1$. $-R_{xy}$ is plotted for $\nu >0$. (b) $R_{xx}$ and $R_{xy}$ measured as a function of magnetic field $B$ at the hole density of $n=3.2\times {10}^{11}{\mathrm{cm}}^{-2}$ in samples $S1$ (solid line) and $S2$ (dashed line). Numbers above horizontal lines indicate the corresponding filling factors.Reuse & Permissions

Figure 3

(a) $R_{xx}$ and $R_{xy}$ measured in sample $S1$ as a function of $B$ at fixed density of $1.9\times {10}^{11}{\mathrm{cm}}^{-2}$ (dotted line) and $0.96\times {10}^{11}{\mathrm{cm}}^{-2}$ (solid line). (b) $R_{xx}$ and $R_{xy}$ measured in sample $S3$ as a function of magnetic field $B$ at fixed density of $0.8\times {10}^{11}{\mathrm{cm}}^{-2}$. Numbers with vertical lines indicate the corresponding filling factors. The straight horizontal lines indicate the expected $R_{xy}$ value for the $1/3$ FQH state. (c) $R_{xx}$ as a function of filling factor at $B=12–14\mathrm{T}$ measured in sample $S2$. (d) $R_{xx}$ as a function of filling factor at $B=12–14\mathrm{T}$ measured in sample $S1$. The letters $A$, $B$ and $C$ with vertical lines indicate minima corresponding to filling factors 1, $2/3$, and $1/3$ respectively. (e) Landau fan diagram $R_{xx}(V_g,B)$ at $T=1.7\mathrm{K}$ measured in sample $S1$. The dark blue lines indicate minima in $R_{xx}$.Reuse & Permissions

Figure 4

(a) $R_{xx}$ measured at different temperatures at 14 T for sample $S1$. (b) Arrhenius plots of $R_{xx}^{\min }$ versus $1/T$ at different fields at $\nu =1/3$ FQH state for sample $S1$. The straight lines are linear fits to the data at the high-temperature activation range. (c) $R_{xx}$ measured at different temperatures at 14 T for sample $S2$. (d) The activation gap as a function of field for two samples: $S1$ and $S2$. The dashed lines are fits to $B$ and the dotted lines are fits to $\sqrt{B}$.Reuse & Permissions