▎ 摘　　要

The dynamical generation of a fermion gap in graphene is studied at the infra-red Lorentz-invariant fixed point where the system is described by an effective relativistic-like field theory: reduced QED(4,3) with N four-component fermions (N = 2 for graphene), where photons are (3+ 1) dimensional and mediate a fully retarded interaction among (2 + 1)-dimensional fermions. A correspondence between reduced QED(4,3) and QED 3 allows us to derive an exact gap equation for QED (4,3) up to next-to-leading order. Our results show that a dynamical gap is generated for a > a(c), where 1.03 < a(c) < 1.08 in the case N = 2 or for N < N-c where N-c is such that a(c) -> infinity and takes the values 3.24 < N-c < 3.36. The striking feature of these results is that they are in good agreement with values found in models with instantaneous Coulomb interaction (including lattice simulations). At the fixed point, alpha = 1/137 << a(c), and the system is therefore in the semimetallic regime in accordance with experiments.