Orientational bond and Néel order in the two-dimensional ionic Hubbard model

Abstract

Unconventional phases often occur where two competing mechanisms compensate. An excellent example is the ionic Hubbard model where the alternating local potential $\delta$, favoring a band insulator (BI), competes with the local repulsion $U$, favoring a Mott insulator (MI). By continuous unitary transformations we derive effective models in which we study the softening of various excitons. The softening signals the instability towards new phases that we describe on the mean-field level. On increasing $U$ from the BI in two dimensions, we find a bond-ordered phase breaking orientational symmetry due to a d-wave component. Then, antiferromagnetic order appears coexisting with the d-wave bond order. Finally, the d-wave order vanishes and a Néel-type MI persists.

8 pages, 7 figures

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• Derivation of the t-J model for finite doping
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• Singlet exciton condensation and bond-order-wave phase in the extended Hubbard model
• Multi-channel fluctuating field approach to competing instabilities in interacting electronic systems
• Self-Energy Dispersion in the Hubbard Model
• Generalization of Lieb-Wu wave function inspired by one-dimensional ionic Hubbard model
• From explicit to spontaneous charge order and the fate of antiferromagnetic quantum Hall state
• Semiconductor of spinons: from Ising band insulator to orthogonal band insulator
• Extracting quantum-critical properties from directly evaluated enhanced perturbative continuous unitary transformations
• High-Temperature Quantum Anomalous Hall Effect in Buckled Honeycomb Antiferromagnets