Staggered Virtual-Loop-Current Order in Pseudospin-1 Dirac Flat Bands

Abstract

Although interactions are known to generate exotic phases in pseudospin-1/2 flat-band Dirac materials, it remains an open question whether the higher-pseudospin systems could realize entirely new types of orders and, if so, how such orders are governed by the nature of the underlying Dirac states. Here, we demonstrate that short-range interactions can drive a staggered virtual-loop-current (SVLC) order together with a $\sqrt{3}\times\sqrt{3}$ charge order in a partially filled pseudospin-1 Dirac flat band of the dice lattice. The virtual loop currents are shown to originate from interaction-driven quantum fluctuations of charge densities and exhibit alternating circulation between the neighboring triangular plaquettes. The resulting spontaneous time-reversal symmetry breaking is found to induce finite intrinsic anomalous Hall conductivity and orbital magnetization. The SVLC state is shown to be the lowest energy solution in restricted real-space Hartree-Fock calculations in the weakly interacting regime. The pseudospin-1 Dirac cones enter the SVLC order through the equivalence of their flat-band wavefunctions, and unlike the pseudospin-1/2 Dirac systems, do not rely on the presence of well-defined low-energy valleys in the electronic spectrum. Our study establishes higher-pseudospin Dirac systems as a new platform for investigating exotic emergent orders in flat-band physics.