Effects of electron-electron interactions on nontrivial flat bands in graphene nanoribbon networks

We theoretically study the ground state of graphene nanoribbon networks (GNR networks), which are periodically arranged networks of graphene nanoribbon junctions, when electron-electron interactions are present. The GNR network exhibits a variety of band structures depending on the junction structure, with a two-electron localized junction structure exhibiting an hourglass-shaped band composed of flat bands and graphene-like bands [1]. We have calculated the ground state for this structure using the Hatree-Fock approach. As a result, several ordered structures including spin/charge/orbital ordered states are found in the strong electron-electron interaction regime. Depending on the order structure, the flat band can be dispersed, form a gap, or transform into a tilted Dirac cone.

[1] G. Tamaki, T. Kawakami, M. Koshino, Phys. Rev. B 101, 205311 (2020).