Flat bands without twists: periodic holey graphene

TL;DR

This paper demonstrates that periodic holey graphene can host flat electronic bands and induce symmetry-breaking effects, providing a simpler alternative to twisted systems for exploring correlated quantum phases.

Contribution

It introduces a method to generate flat bands in holey graphene through periodic lattice holes, without the need for twisting, and analyzes the resulting electronic properties and symmetries.

Findings

Flat bands emerge in holey graphene due to periodic holes.

Symmetry breaking induces gaps and Berry curvature.

Flat bands can be engineered by controlling hole periodicity.

Abstract

\textit{Holey Graphene} (HG) is a widely used graphene material for the synthesis of high-purity and highly crystalline materials. In this work, we explore the electronic properties of a periodic distribution of lattice holes, demonstrating the emergence of flat bands with compact localized states. It is shown that the holes break the bipartite sublattice and inversion symmetries, inducing gaps and a nonzero Berry curvature. Moreover, the folding of the Dirac cones from the hexagonal Brillouin zone (BZ) to the holey superlattice rectangular BZ of HG with sizes proportional to an integer $n$ times the graphene's lattice parameter leads to a periodicity in the gap formation such that $n \equiv 0$ (mod $3$). Meanwhile, it is shown that if $n \equiv \pm 1$ (mod $3$), a gap emerges where Dirac points are folded along the $\Gamma-X$ path. The low-energy hamiltonian for the three central bands is also obtained, revealing that the system behaves as an effective $\alpha-\mathcal{T}_{3}$ graphene material. Therefore, a simple protocol is presented here that allows obtaining flat bands at will. Such bands are known to increase electron-electron correlated effects. This work provides an alternative system, much easier to build than twisted systems, to obtain highly correlated quantum phases.