Quasiparticle scattering off phase boundaries in epitaxial graphene

TL;DR

This study uses scanning tunneling microscopy to analyze how quasiparticles scatter at the edges of epitaxial graphene on SiC, revealing edge-specific scattering patterns and the influence of doping on local electronic structures.

Contribution

It provides new insights into edge-dependent quasiparticle scattering in epitaxial graphene and offers an alternative interpretation of LDOS superstructures near edges.

Findings

Armchair edges promote intervalley quasiparticle scattering.

Doping causes complex LDOS patterns combining superstructure and beating modulation.

Absence of intervalley scattering at zig-zag edges and graphene junctions.

Abstract

We investigate the electronic structure of terraces of single layer graphene (SLG) by scanning tunneling microscopy (STM) on samples grown by thermal decomposition of 6H-SiC(0001) crystals in ultra-high vacuum. We focus on the perturbations of the local density of states (LDOS) in the vicinity of edges of SLG terraces. Armchair edges are found to favour intervalley quasiparticle scattering, leading to the (\surd3\times\surd3)R30{\deg} LDOS superstructure already reported for graphite edges and more recently for SLG on SiC(0001). Using Fourier transform of LDOS images, we demonstrate that the intrinsic doping of SLG is responsible for a LDOS pattern at the Fermi energy which is more complex than for neutral graphene or graphite, since it combines local (\surd3\times\surd3)R30{\deg} superstructure and long range beating modulation. Although these features were already reported by Yang et al. Nanoletters 10, 943 (2010), we propose here an alternative interpretation based on simple arguments classically used to describe standing wave patterns in standard two-dimensional systems. Finally, we discuss the absence of intervalley scattering off other typical boundaries: zig-zag edges and SLG/bilayer graphene junctions.