Electronic Structure of Quantum Materials

We have made nitrogen core-doped graphene nanoribbons. In these GNRs, the nitrogen atoms are forced into positions that are normally occupied by carbon atoms. The valence mismatch causes the nitrogen atoms to shed their electrons, with some electrons being absorbed by the gold substrate and the others behaving as little magnets. Although screened by magnetic interactions of electrons in the gold through the Kondo effect (making the GNR a Kondo lattice), interactions between neighboring spins are revealed when the nanoribbons are slightly peeled off the surface.[5]

We have recently explored the synthesis and the electronic structure of a new type of graphene nanoribbon: the cyclobutadienoid GNR. In addition to the usual carbon hexagons, this ribbon features carbon tetragons, or four-membered rings. These highly unusual motifs are associated with chemical reactivity (which makes their synthesis challenging) but new electronic behavior as well. In our collaboration with the group of Colin Nuckolls as Columbia University, we reveal not only the successful preparation of such nanoribbons, but we also reveal a general blueprint for quantum engineering electronic properties based on these four-membered rings as new functional elements.[6]

The electronic structure and quantum mechanical wave functions inside graphene nanoribbons satisfy numerous interesting fundamental symmetries. Having knowledge of the interplay of the structure of a nanoribbon and electronic behavior is important to rationally design electronic components with well-defined functionality. Our collaborators from the group of Steven Louie discovered that modulating the width of a graphene nanoribbon in a well-defined way necessarily gives rise to localized electronic states, which can be explained in the mathematical framework of topology. We have used this insight to create quantum dots inside graphene nanoribbons: structures in which we have captured a number of electrons in the center section.[7]