Topological bands in two-dimensional orbital-active bipartite lattices

Abstract

The search for large gap quantum spin Hall (QSH) and quantum anomalous Hall (QAH) insulators is important both for fundamental and practical interests. The degenerate multi-orbitals $p_x,p_y$ in honeycomb lattice provides a paradigm for QSH state with a boosted topological gap of the first order in atomic spin-orbit coupling. By using elementary band representation, we explore the feasibility of this mechanism for QSH in general two-dimensional lattices, and find that the biparticle lattices with $C_{3v}$ or $C_{4v}$ symmetry and degenerate multi-orbitals could work. We further provide concrete tight-binding models on honeycomb, kagome and square lattices to demonstrate the desired topological physics. By introducing ferromagnetism into QSH state, we extend the mechanism to QAH state with a boosted gap. The QSH and QAH states can be achieved when Fermi level is at integer filling only for honeycomb lattice, but at certain fractional filling for other lattices. We conclude with a brief discussion on the possible material venues for such mechanism.