Temperature-Dependent Transport in Suspended Graphene

The resistivity of ultraclean suspended graphene is strongly temperature ($T$) dependent for $5<T<240\mathrm{K}$. At $T\sim 5\mathrm{K}$ transport is near-ballistic in a device of $\sim 2\mu \mathrm{m}$ dimension and a mobility $\sim 170000{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$. At large carrier density, $n>0.5\times {10}^{11}{\mathrm{cm}}^{-2}$, the resistivity increases with increasing $T$ and is linear above 50 K, suggesting carrier scattering from acoustic phonons. At $T=240\mathrm{K}$ the mobility is $\sim 120000{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$, higher than in any known semiconductor. At the charge neutral point we observe a nonuniversal conductivity that decreases with decreasing $T$, consistent with a density inhomogeneity $<{10}^8{\mathrm{cm}}^{-2}$.