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

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 [Gomes et al., Nature (London) 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 in the Bogoliubov–de Gennes equations, 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 mathematical analogs of Majorana fermions in some superconducting states. The subgap states bind a fractional charge of e/2 to the vortex core, in effect delocalizing a single electron between two vortex cores, or between one vortex core and the system boundary. The Kekule texture as realized in the molecular graphene system realizes three different domain types, and we show that a Y junction between them realizes the coveted Kekule vortex.