  The electrical conductivity of suspended graphene has recently been measured
for the first time, and found to behave as \sigma ~ \sqrt{|n|} as expected for
Dirac quasiparticles at large carrier density. The charge inhomogeneity is
strongly reduced in suspended samples, which revealed an unexpected insulating
trend in \sigma(T). Above a transitional density n*, the temperature dependence
was found to revert to metallic. We show that these features of the DC
conductivity are consistent with a simple model of gapped Dirac quasiparticles,
with specific signatures of a gap in the vicinity of the charge-neutrality
point. Our findings are reminiscent of the conductivity profile in
semiconducting materials, exhibiting a thermal activation for T \geq \tilde T
and a weakly T-dependent background for T \leq \tilde T, where \tilde T is
given by the saturation density \tilde n associated with the residual charge
inhomogeneity. We discuss possible origins of a bandgap in graphene as well as
alternative scenarios.
