Velocity renormalization in graphene from lattice monte carlo

We compute the Fermi velocity of the Dirac quasiparticles in clean graphene at the charge neu- Trality point for strong Coulomb coupling ag. We perform a Lattice Monte Carlo calculation within the low-energy Dirac theory, which includes an instantaneous, long-range Coulomb in- Teraction. We find a renormalized Fermi velocity vFR > vF, where vF ≃ c=300. Our results are consistent with a momentum-independent vFR which increases approximately linearly with ag, although a logarithmic running with momentum cannot be excluded at present. At the predicted critical coupling agc for the semimetal-insulator transition due to excitonic pair formation, we find vFR=vF ≃ 3:3, which we discuss in light of experimental findings for vFR=vF at the charge neutrality point in ultra-clean suspended graphene