Bridging the Physics and Chemistry of graphene. From Huckel aromaticity to Dirac cones and topological insulators

TL;DR

This paper reveals that graphene's exotic properties stem from aromaticity and shell structure, linking molecular aromaticity to macroscopic topological phenomena like Dirac cones and edge states.

Contribution

It establishes a molecular-level understanding of graphene's properties through aromaticity, shell structure, and topology, connecting chemistry with condensed matter physics.

Findings

Graphene is a coherent arrangement of benzene molecules.

Aromaticity drives the macroscopic properties of graphene.

Topological gapless edge states in nanographenes are not spin polarized.

Abstract

By bridging graphene and benzene through a well-defined sequence of polycyclic aromatic hydrocarbons and their inherent shell structure, J. Phys. Chem. C, 2018, 122, 17526, it is shown that graphene is actually a coherent arrangement of interwoven benzene molecules, which are coordinated by aromaticity, shell structure and topology, all interrelated. The exotic properties of graphene are in fact macroscopic manifestations of aromaticity. At the molecular level this is revealed as a dynamical flipping of the atomic pz-orbitals belonging to different sublattices, leading to a dynamical interchange between aromatic and non-aromatic rings, associated with frontier occupied-unoccupied orbitals or valence-conduction bands interchange with opposite parities, in full agreement with many-body and topological insulators theory. Such dynamical interchange or coupling is driven by inversion symmetry-breaking, activated through geometrical frustration between sublattice and space group symmetry. This, for rectangular nanographenes, in contrast to hexagonal, leads to topological gapless edge states, which, contrary to opposite claims, are not spin polarized.