Hot-Carrier Seebeck Effect: Diffusion and Remote Detection of Hot Carriers in Graphene

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 <i>V</i>_NL across the remaining (detector) leads. Due to the nonlocal character of the measurement, <i>V</i>_NL is exclusively due to the Seebeck effect. Remarkably, a departure from the ordinary relationship between Joule power <i>P</i> and <i>V</i>_NL, <i>V</i>_NL ∼ <i>P</i>, becomes readily apparent at low temperatures, representing a fingerprint of hot-carrier dominated thermoelectricity. By studying <i>V</i>_NL 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