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The interference patterns arising from the scattering of quasiparticles in epitaxial graphene grown on SiC(0001) were investigated by scanning tunneling spectroscopy. Energy resolved maps of the differential conductance reveal modulations of the local density of states on two different length scales. The two characteristic wavelengths are determined by scattering wavevectors that connect contours of constant energy in the graphene reciprocal space, which are normally suppressed due to the symmetries in graphene’s electronic structure. In this study, the presence of lattice defects is shown to mix wavefunctions of different symmetries, thereby affecting the allowed scattering of the Dirac quasiparticles. The regions of constructive interference are shown to exhibit sharp resonances in the energy spectrum of quasiparticle states, and provide an association between the standing wave patterns and localized states. |