  Early experiments on alkali-doped graphene demonstrated that the dopant
adatoms modify the conductivity of graphene significantly, as extra carriers
enhance conductivity while Coulomb scattering off the adatoms suppresses it.
However, conductivity probes the overall scattering rate, so a dominant channel
associated with long-range Coulomb scattering will mask weaker short-range
channels. We present weak localization measurements of epitaxial graphene with
lithium adatoms that separately quantify intra- and intervalley scattering
rates, then compare the measurements to tight-binding calculations of expected
rates for this system. The intravalley rate is strongly enhanced by Li
deposition, consistent with Coulomb scattering off the Li adatoms. A
simultaneous enhancement of intervalley scattering is partially explained by
extra carriers in the graphene interacting with residual disorder. But
differences between measured and calculated rates at high Li coverage may
indicate adatom-induced modifications to the band structure that go beyond the
applied model. Similar adatom-induced modifications of the graphene bands have
recently been observed in ARPES, but a full theoretical understanding of these
effects is still in development.
