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SU(3) topological insulators in the honeycomb lattice
摘要： We investigate realizations of topological insulators with spin-1 bosons loaded in a honeycomb optical lattice and subjected to a SU(3) spin-orbit coupling—a situation which can be realized experimentally using cold atomic gases. In this paper, we focus on the topological properties of the single-particle band structure, namely, Chern numbers (lattice with periodic boundary conditions) and edge states (lattice with strip geometry) and their connection to time-reversal symmetry and the sublattice symmetry. While SU(2) spin-orbit couplings always lead to time-reversal symmetric tight-binding models, and thereby to topologically trivial band structures, suitable SU(3) spin-orbit couplings can break time-reversal symmetry and lead to topologically nontrivial bulk band structures and to edge states in the strip geometry. In addition, we show that one can trigger a series of topological transitions (i.e., integer changes of the Chern numbers) that are speci?c to the geometry of the honeycomb lattice by varying a single parameter in the Hamiltonian.
关键词： sublattice symmetry,SU(3) spin-orbit coupling,honeycomb optical lattice,spin-1 bosons,time-reversal symmetry,edge states,topological insulators,Chern numbers
更新于2025-09-09 09:28:46
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Correlations and electronic order in a two-orbital honeycomb lattice model for twisted bilayer graphene
摘要： The recent observation of superconductivity in proximity to an insulating phase in twisted bilayer graphene (TBG) at small “magic” twist angles has been linked to the existence of nearly ?at bands, which make TBG a fresh playground to investigate the interplay between correlations and superconductivity. The low-energy narrow bands were shown to be well described by an effective tight-binding model on the honeycomb lattice (the dual of the triangular Moiré superlattice) with a local orbital degree of freedom. In this paper, we perform a strong-coupling analysis of the proposed (px, py ) two-orbital extended Hubbard model on the honeycomb lattice. By decomposing the interacting terms in the particle-particle and particle-hole channels, we classify the different possible superconducting, magnetic, and charge instabilities of the system. In the pairing case, we pay particular attention to the two-component (d-wave) pairing channels, which admit vestigial phases with nematic or chiral orders, and study their phenomenology. Furthermore, we explore the strong-coupling regime by obtaining a simpli?ed spin-orbital exchange model which may describe a putative Mott-type insulating state at quarter-?lling. Our mean-?eld solution reveals a rich intertwinement between ferromagnetic and antiferromagnetic orders with different types of nematic and magnetic orbital orders. Overall, our work provides a solid framework for further investigations of the phase diagram of the two-orbital extended Hubbard model in both strong- and weak-coupling regimes.
关键词： spin-orbital exchange model,Hubbard model,twisted bilayer graphene,superconductivity,honeycomb lattice,correlations
更新于2025-09-09 09:28:46
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A Full-Dielectric Chiral Material Based on a Honeycomb Structure
摘要： A uniaxial bianisotropic, full-dielectric structure has been designed and numerically studied. The material is based on a previously published 2D-honeycomb structure. A 3D expansion leads to an e?ective metamaterial showing a typical chiral electromagnetic behavior, i.e., a resonant electromagnetic activity with a small circular dichroism.
关键词： electromagnetic activity,honeycomb structure,full-dielectric,circular dichroism,chiral material
更新于2025-09-09 09:28:46