Thursday, July 4, 2013

1307.0922 (Yasufumi Yamashita et al.)

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

Yasufumi Yamashita, Masaki Tomura, Yuki Yanagi, Kazuo Ueda
We investigate the magnetic and metal(M)-insulator(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 para(P)-, antiferro(AF)-, and ferro-magnetic(F) types, each realized for the large intra-square hopping t1, inter-square 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 U-t1/t2 plane. When t1 = t2, we find that the Dirac cone and nearly flat-band around \Gamma point form the SU(3) multiplet. The SU(3) effective theory well-describes the phase transitions between PI, PM, and AF phases. The PI and AFI phases are characterized by different Berry phases as in polyacetylene or graphene.
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