title: Direct experimental determination of onset of electron-electron interactions in gap opening of zigzag graphene nanoribbons.
abstract: Nanoribbons are model systems for studying nanoscale effects in graphene. For ribbons with zigzag edges, tunable bandgaps have been predicted due to coupling of spin-polarized edge states, which have yet to be systematically demonstrated experimentally. Here we synthesize zigzag nanoribbons using Fe nanoparticle-assisted hydrogen etching of epitaxial graphene/SiC(0001) in ultrahigh vacuum. We observe two gaps in their local density of states by scanning tunnelling spectroscopy. For ribbons wider than 3 nm, gaps up to 0.39 eV are found independent of width, consistent with standard density functional theory calculations. Ribbons narrower than 3 nm, however, exhibit much larger gaps that scale inversely with width, supporting quasiparticle corrections to the calculated gap. These results provide direct experimental confirmation of electron-electron interactions in gap opening in zigzag nanoribbons, and reveal a critical width of 3 nm for its onset. Our findings demonstrate that practical tunable bandgaps can be realized experimentally in zigzag nanoribbons.
authors.affiliation: Department of Physics, University of Wisconsin, 1900 E Kenwood Boulevard, Milwaukee, Wisconsin 53211, USA.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Li
authors.affiliation: Department of Physics, University of Wisconsin, 1900 E Kenwood Boulevard, Milwaukee, Wisconsin 53211, USA.
authors.forename: M X
authors.initials: MX
authors.lastname: Chen
authors.affiliation: Department of Physics, University of Wisconsin, 1900 E Kenwood Boulevard, Milwaukee, Wisconsin 53211, USA.
authors.forename: M
authors.initials: M
authors.lastname: Weinert
authors.affiliation: Department of Physics, University of Wisconsin, 1900 E Kenwood Boulevard, Milwaukee, Wisconsin 53211, USA.
authors.forename: L
authors.initials: L
authors.lastname: Li