Giant edge state splitting at atomically precise graphene zigzag edges

Abstract

Zigzag edges of graphene nanostructures host localized electronic states that are predicted to be spin-polarized. However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunnelling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunnelling spectroscopy, which reveals a pair of occupied/unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with ab initio many-body perturbation theory calculations and reflects the dominant role of electron–electron interactions in these localized states.

Electrical spin manipulation in graphene nanostructures

“…Our findings could be used to manipulate individual pairs of spins in nanographene structures. The independent progress both in spin resonance driven by scanning tunneling microscopes and in the fabrication of atomically defined graphene nanostructures with bottom-up techniques [17,18,62,63] …”

“…The exploration with STM of some of the graphene nanostructures studied here has been demonstrated [17,18,30]. With this approach, the application of an off-plane electric field significantly larger than in conventional field effect transistor geometries is possible.…”

“…Their direct experimental observation by means of scanning tunneling microscopy (STM) has been reported both for the edge states of rectangular nanographenes with short zigzag edges [17] as well as for the individual and for pairs of chemisorbed hydrogen atoms in graphene [29,30]. These sublattice polarized zero modes are expected to host unpaired spin electrons, giving rise to the formation of local moments [24,28,[31][32][33][34][35][36][37][38].…”

“…Interestingly, a class of graphene nanostructures that can be synthesized with bottom-up techniques [17,18] provides naturally, without the need of electrical control of the number of carriers, exchange-coupled unpaired spin electron duets in an environment with a low density of carbon nuclear spins. In Fig.…”

Inhomogeneous strain-induced half-metallicity in bent zigzag graphene nanoribbons

“…Given the superior structural flexibility of graphene, 29 our design is promising for a practical realization given the present experimental advances in the fabrication of GNR samples with sharp zigzag edges 30,31 and in controlling the interplay between GNRs and substrates. 32 …”