larger by two orders of magnitude or more is sufficient. The model is therefore more amenable to experimental realization.'
author:
- 'I. Snyman'
date: April 2009
title: 'The gapped state of a carbon mono-layer in periodic magnetic and electric fields'
---

The filled conduction band and the empty valence band of a carbon mono-layer (graphene) touch at two inequivalent points in the Brillouin zone.[@Cas09] Regions of the Brillouin zone in the vicinity of these points are called valleys. In each of the two valleys, low energy excitations are described by a two-dimensional massless Dirac equation. As a consequence, electrons in graphene can propagate through electrostatic potential barriers. In the jargon of relativistic quantum mechanics, this is known as Klein tunneling.[@Kat06; @Been07] When a gap is induced between the valence and conduction band, Klein tunneling is suppressed and the electronic properties of graphene change radically. Several distinct situations have been uncovered:

Recently a method for producing a band insulating state was demonstrated experimentally.[@Zhou07] It involves growing the graphene sample on an appropriate substrate that induces a potential energy difference between the two triangular sublattices that constitute the sample’s honeycomb lattice. In a seminal paper by Haldane,[@Hal88] it was demonstrated that graphene’s 