  We investigate hot carrier propagation across graphene using an electrical
nonlocal injection/detection method. The device consists of a monolayer
graphene flake contacted by multiple metal leads. Using two remote leads for
electrical heating, we generate a carrier temperature gradient that results in
a measurable thermoelectric voltage VNL across the remaining (detector) leads.
Due to the nonlocal character of the measurement, VNL is exclusively due to the
Seebeck effect. Remarkably, a departure from the ordinary relationship between
Joule power P and VNL, VNL ~ P, becomes readily apparent at low temperatures,
representing a fingerprint of hot-carrier dominated thermoelectricity. By
studying VNL as a function of bias, we directly determine the carrier
temperature and the characteristic cooling length for hot-carrier propagation,
which are key parameters for a variety of new applications that rely on
hot-carrier transport.
