Temperature dependent transport in suspended graphene

The resistivity of ultra-clean suspended graphene is strongly temperature dependent for 5K<T<240K. At T~5K transport is near-ballistic in a device of ~2um dimension and a mobility ~170,000 cm^2/Vs. At large carrier density, n>0.5*10^11 cm^-2, the resistivity increases with increasing T and is linear above 50K, suggesting carrier scattering from acoustic phonons. At T=240K the mobility is ~120,000 cm^2/Vs, higher than in any known semiconductor. At the charge neutral point we observe a non-universal conductivity that decreases with decreasing T, consistent with a density inhomogeneity <10^8 cm^-2.