  We demonstrate a flip-chip device for performing low-temperature
acoustoelectric measurements on exfoliated two-dimensional materials. With this
device, we study gate-tunable acoustoelectric transport in an exfoliated
monolayer graphene device, measuring the voltage created as high-frequency
surface acoustic waves dynamically drive the graphene charge carriers, the
density of which we simultaneously control with a silicon back-gate. We
demonstrate ambipolar dependence of the acoustoelectric signal, as expected
from the sign of the graphene charge carriers. We observe a marked reduction in
the magnitude of the acoustoelectric signal over a well-defined range of
density in the vicinity of charge neutrality, which we attribute to a spatially
heterogeneous charge-disorder landscape not directly revealed by conventional
transport measurements.
