  An extended Hubbard model on a honeycomb lattice with two orbitals per site
at charge neutrality is investigated with unbiased large-scale quantum Monte
Carlo simulations. The Fermi velocity of the Dirac fermions is renormalized as
the cluster charge interaction increases, until a mass term emerges and a
quantum phase transition from Dirac semi-metal to valence bond solid (VBS)
insulator is established. The quantum critical point is discovered to belong to
3D $N=4$ Gross-Neveu chiral XY universality with the critical exponents
obtained at high precision. Further enhancement of the interaction drives the
system into two different VBS phases, the properties and transition between
them are also revealed. Since the model is related to magic-angle twisted
bilayer graphene, our results may have relevance towards the symmetry breaking
order at the charge neutrality point of the material, and associate the wide
range of universal strange metal behavior around it with quantum critical
fluctuations.
