Dirac fermions with plaquette interactions. I. SU(2) phase diagram with Gross-Neveu and deconfined quantum criticalities

We investigate the ground state phase diagram of an extended Hubbard model with a pi-flux hopping term at half filling on a square lattice, with unbiased large-scale auxiliary-field quantum Monte Carlo simulations. As a function of interaction strength, there emerges an intermediate phase which realizes two interaction-driven quantum critical points, with the first between the Dirac semimetal and an insulating phase of weak valence bond solid (VBS) order, and the second separating the VBS order and an antiferromagnetic insulating phase. These intriguing quantum critical points are respectively bestowed with Gross-Neveu and deconfined quantum criticalities, and the critical exponents eta VBS = 0.6(1) and eta AFM = 0.58(3) at a deconfined quantum critical point satisfy the conformal field theory bootstrap bound. We also investigate the dynamical properties of the spin excitation and find the spin gap open near the first transition and closed at the second. The relevance of our findings in realizing deconfined quantum criticality in fermion systems and the implication to lattice models with further extended interactions such as those in quantum moire systems, are discussed.

Automated summary

We investigate the ground state phase diagram of an extended Hubbard model with a pi-flux hopping term at half filling on a square lattice using large-scale auxiliary-field quantum Monte Carlo simulations. We find an intermediate phase with two interaction-driven quantum critical points, characterized by Gross-Neveu and deconfined quantum criticalities. We also study the dynamical properties of the spin excitation and find the spin gap opening and closing at the two transitions. The relevance of these findings to deconfined quantum criticality in fermion systems and lattice models with further extended interactions is discussed.