  Commensurate-incommensurate transitions are ubiquitous in physics and are
often accompanied by intriguing phenomena. In few-layer graphene (FLG) systems,
commensurability between honeycomb lattices on adjacent layers is regulated by
their relative orientation angle theta, which is in turn dependent on sample
preparation procedures. Because incommensurability suppresses inter-layer
hybridization, it is often claimed that graphene layers can be electrically
isolated by a relative twist, even though they are vertically separated by a
fraction of a nanometer. We present a theory of interlayer transport in FLG
systems which reveals a richer picture in which the specific conductance
depends sensitively on theta, single-layer Bloch state lifetime, in-plane
magnetic field, and bias voltage. We find that linear and differential
conductances are generally large and negative near commensurate values of
theta, and small and positive otherwise.
