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

TL;DR

This paper demonstrates a nonlocal thermoelectric measurement technique in graphene to detect hot-carrier propagation, revealing unique temperature-dependent effects and enabling the determination of carrier temperature and cooling length.

Contribution

It introduces a novel electrical nonlocal method to study hot-carrier diffusion and remote detection in graphene, highlighting temperature-dependent thermoelectric effects.

Findings

Hot-carrier thermoelectricity dominates at low temperatures.

The method measures carrier temperature and cooling length directly.

Departure from P ~ VNL relationship indicates hot-carrier effects.

Abstract

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.