Symmetry breaking in epitaxial graphene probed by ARPES

The energy bands of $n$-doped graphene on SiC(0001) have been observed to deviate significantly from the expected conical shape near the Dirac crossing[Bostwick et al 2007, Zhou et al 2007]. Two scenarios have been proposed to explain these deviations, either as originated from the real part of the electronic self-energy due to many body interactions[Bostwick et al], or from ``A-B'' symmetry-breaking due to chemical interactions between the graphene and the underlying layer[Zhou et al]. In this talk we present a number of arguments against the A-B symmetry breaking scenario, among which is the observed \textbf{k}-dependent intensity of the Fermi surface as measured by ARPES. We show that the observed intensity distribution is directly sensitive to the degree of A-B symmetry breaking and show that the upper limit for an energy gap in graphene on SiC is much smaller than the observed deviations in the band structure.