Realization of a vortex in the Kekule texture of molecular graphene at a Y junction where three domains meet

Abstract

Following the recent realization of an artificial version of Graphene in the electronic surface states of copper with judiciously placed carbon monoxide molecules inducing the honeycomb lattice symmetry (K. K. Gomes et al., Nature 483, 306 (2012)), we demonstrate that these can be used to realize a vortex in a Kekule texture of the honeycomb lattice. The Kekule texture is mathematically analogous to a superconducting order parameter, opening a spectral gap in the massless Dirac point spectrum of the Graphene structure. The core of a vortex in the texture order parameter, supports subgap states, which for this system are analogs of Majorana fermions in some superconducting states. In particular, the electron charge bound to a single vortex core is effectively fractionalized to a charge of $e/2$. The Kekule texture as realized in the molecular Graphene system realizes 3 different domain types, and we show that a Y-junction between them realizes the coveted Kekule vortex.