Competition between band and Mott insulators in the bilayer Hubbard model: A dynamical cluster approximation study

초록

We investigate the nature of the insulating phases in a bilayer Hubbard model with intralayer coupling t and interlayer coupling t(perpendicular to) at large interaction strength U/t and half-filling. We consider a dynamical cluster approximation with a cluster size of N-c = 2 x 4, where short-range spatial fluctuations as well as on-site dynamical fluctuations are emphasized. By varying the band splitting (t(perpendicular to)/t), we find that at t(perpendicular to)/t similar or equal to 1.5 the Mott behavior is rapidly suppressed in the momentum sectors (pi,0) and (0,pi). At t(perpendicular to)/t similar or equal to 2.5, Mott features dominate in the momentum sectors (pi,pi) of the bonding band and (0,0) of the antibonding band, and at t(perpendicular to)/t similar or equal to 3.0, a tiny scattering rate is observed in all momentum sectors at the Fermi level, indicating a transition from a Mott to a band insulator. We attribute such a momentum-dependent evolution of the insulating behavior to the competition and cooperation between short-range spatial fluctuations and interlayer coupling t(perpendicular to) with the help of the Coulomb interaction U. Finally, we also discuss the possible appearance of non-Fermi liquid behavior away from half-filling.

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