Direct measurement of strain-driven Kekulé distortion in graphene and its electronic properties.

Kekulé distortion in graphene is a subject of extensive theoretical studies due to its non-trivial material properties. Yet, experimental observation of its formation mechanism and electronic structures is still elusive. Here, we used scanning tunneling microscopy to visualize two different phases of the Kekulé distortion in graphene along with experimental evidence that local strain is responsible for the formation of such distortions. In addition, we directly measured the electronic structures of the two phases of the Kekulé distortion in graphene revealing that one opens an energy gap whereas the other maintains a linear density profile. These are consistent with the calculated band structures of the two phases of the Kekulé distortion, respectively, providing a direct verification of the theoretical predictions.