SU(3) Dirac electrons in the 1/5-depleted square-lattice Hubbard model at 1/4 filling

TL;DR

This paper explores the magnetic and metal-insulator phase diagram of a 1/5-depleted square-lattice Hubbard model at quarter filling, revealing SU(3) symmetry and phase transitions characterized by Berry phases.

Contribution

It introduces an SU(3) effective theory for describing phase transitions in the model and identifies six phases, including Dirac and flat bands, at specific hopping parameters.

Findings

Identification of six distinct phases in the U-t1/t2 plane.

Discovery of SU(3) symmetry when t1 equals t2.

Characterization of Berry phases in different insulating phases.

Abstract

We investigate the magnetic and metal-insulator (M-I) phase diagram of the 1/5-depleted square-lattice Hubbard model at 1/4 filling by the mean-field approximation. There exist three magnetic phases of nonmagnetic (N), antiferromagnetic (AF), and ferromagnetic (F) types, each realized for the large intrasquare hopping t1, intersquare hopping t2, and Coulomb interaction U, respectively. Within each magnetic phase, the M-I transition of Lifshitz type emerges and, finally, six kind of phases are identified in the U-t1/t2 plane. When t1=t2, we find that the Dirac cone and nearly flat band around the Gamma point form the SU(3) multiplet. The SU(3) effective theory well describes the phase transitions between NI, paramagnetic-metal (PM), and AF phases. The NI and AFI phases are characterized by different Berry phases as in polyacetylene or graphene.