Merging of the Dirac points in electronic artificial graphene

TL;DR

This paper demonstrates that the merging of Dirac points, predicted in strained graphene, can be observed in electronic artificial graphene created from a 2D electron gas with a triangular lattice of antidots, indicating a topological phase transition.

Contribution

It provides a numerical and analytical study showing Dirac point merging in artificial graphene under strain, which has not been observed in natural graphene.

Findings

Dirac points shift and merge under strain in artificial graphene

Merging leads to an energy gap, indicating a topological phase transition

Results are consistent with recent experimental observations

Abstract

Theory predicts that graphene under uniaxial compressive strain in an armchair direction should undergo a topological phase transition from a semimetal into an insulator. Due to the change of the hopping integrals under compression, both Dirac points shift away from the corners of the Brillouin zone towards each other. For sufficiently large strain, the Dirac points merge and an energy gap appears. However, such a topological phase transition has not yet been observed in normal graphene (due to its large stiffness) neither in any other electronic system. We show numerically and analytically that such a merging of the Dirac points can be observed in electronic artificial graphene created from a two-dimensional electron gas by application of a triangular lattice of repulsive antidots. Here, the effect of strain is modeled by tuning the distance between the repulsive potentials along the armchair direction. Our results show that the merging of the Dirac points should be observable in a recent experiment with molecular graphene.