Novel electronic wave interference patterns in nanographene sheets

Superperiodic patterns extending over a large distance in a nanographene sheet observed using a scanning tunnelling microscope are discussed in terms of the interference of electronic wavefunctions. The period and the amplitude of the oscillations decrease spatially in one direction. We explain the superperiodic patterns with a static linear potential, theoretically. In the k . p model, the oscillation period decreases, and agrees with experiments. The spatial difference of the static potential is estimated as 1.3 eV for 200 nm in distance, and this value seems to be reasonable preserving for the potential difference under the action of perturbations, for example, phonon fluctuations and impurity scatterings. It turns out that the long-distance oscillations arise from the band structure of the two-dimensional graphene sheet.