  We study the Hubbard model on the honeycomb lattice in the vicinity of the
quantum critical point by means of a multiband formulation of the Dual Fermion
approach. Beyond the strong local correlations of the dynamical mean field,
critical fluctuations on all length scales are included by means of a ladder
diagram summation. Analysis of the susceptibility yields an estimate of the
critical interaction strength of the quantum phase transition from a
paramagnetic semimetal to an antiferromagnetic insulator, in good agreement to
other numerical methods. We further estimate the crossover temperature to the
renormalized classical regime. Our data imply that, at large interaction
strengths, the Hubbard model on the honeycomb lattice behaves like a quantum
nonlinear sigma model, while being in a non-Fermi liquid state.
