In conventional measurements of the resistance of a two-dimensional (2D) layer an electrical current is driven through the layer and the voltage drop along the layer is measured. In contrast, Coulomb drag studies are performed on two closely spaced but electrically isolated layers, where a current I 1 is driven through one of the layers (active layer) and the voltage drop V 2 is measured along the other (passive) layer (Fig. 1). The origin of this voltage is electron-electron (e-e) interaction between the layers, which creates a 'frictional' force that drags electrons in 1

No abstract

We have experimentally studied the nonlinear nature of electrical conduction in monolayer graphene devices on silica substrates. This nonlinearity manifests itself as a nonmonotonic dependence of the differential resistance on applied dc voltage bias across the sample. At temperatures below ∼70 K, the differential resistance exhibits a peak near zero bias that can be attributed to self-heating of the charge carriers. We show that the shape of this peak arises from a combination of different energy dissipation mechanisms of the carriers. The energy dissipation at higher carrier temperatures depends critically on the length of the sample. For samples longer than 10 μm the heat loss is shown to be determined by optical phonons at the silica-graphene interface. Graphene is a promising material for electronic applications because of its high electrical and thermal conductivities. 1 A limiting intrinsic room-temperature mobility of graphene fieldeffect transistors of ∼2 × 10 5 cm 2 /V s has been estimated 2 and approached experimentally. 3 Its high thermal conductivity, 4 far exceeding that of copper, holds great promise for heat management in electronics. 5 Fully realizing this potential requires an understanding of the scattering mechanisms in graphene, particularly electron-phonon scattering, which becomes increasingly important with increasing temperature and device currents.Several different techniques have been used to study the coupling between charge carriers and phonons in graphene. Measurements of the temperature dependence of the resistance have shown that at low temperatures, T < 150 K, electronphonon scattering is dominated by longitudinal acoustic phonons, 2,6-8 resulting in a linear temperature dependence of the resistivity. At higher temperatures the resistivity becomes strongly temperature dependent, possibly due to ripples in the graphene membrane 8 or coupling with remote interfacial phonons (RIPs) at the SiO 2 surface. 2,9 This latter scattering mechanism has been put forward as an important heat dissipation mechanism in carbon nanotube and graphene devices. [10][11][12] Measurements of the current saturation in graphene lend support to the hypothesis that these RIPs are an important scattering mechanism, 13 although another study identifies scattering with optical phonons intrinsic to the graphene lattice 14 as the dominant saturation mechanism.In this Rapid Communication, we report electrical measurements of monolayer graphene field-effect transistors in the high-current regime at temperatures between 4 and 200 K. We show that overheating of the charge carriers results in a nonmonotonic dependence of the differential resistance on source-drain bias. By correlating this dependence with the measured temperature dependence of the differential resistance, we test different models of thermal transport and electron-phonon coupling, and demonstrate that energy dissipation is dominated by coupling to the remote interfacial phonons in the silica substrate.Graphene flakes were mechanically exfoliated onto ...