  We report on quantum-interference measurements in top-gated Hall bars of
monolayer graphene epitaxially grown on the Si face of SiC, in which the
transition from negative to positive magnetoresistance was achieved varying
temperature and charge density. We perform a systematic study of the quantum
corrections to the magnetoresistance due to quantum interference of
quasiparticles and electron-electron interaction. We analyze the contribution
of the different scattering mechanisms affecting the magnetotransport in the
$-2.0 \times 10^{10}$ cm$^{-2}$ to $3.75 \times 10^{11}$ cm$^{-2}$ density
region and find a significant influence of the charge density on the
intravalley scattering time. Furthermore, we observe a modulation of the
electron-electron interaction with charge density not accounted for by present
theory. Our results clarify the role of quantum transport in SiC-based devices,
which will be relevant in the development of a graphene-based technology for
coherent electronics.
