Drag of electrons in graphene by substrate surface polar phonons

TL;DR

This paper develops a theory for electron drag by substrate surface polar phonons in graphene and finds that its contribution to thermopower is minor compared to diffusion, supporting Mott's law.

Contribution

The authors present the first complete theoretical model of SPP drag in graphene, quantifying its impact on thermopower and explaining its small magnitude.

Findings

SPP drag contribution to thermopower is an order of magnitude lower than diffusion.

Low SPP occupation number and short phonon mean free path limit drag effects.

Experimental thermopower in graphene aligns with Mott's law, indicating diffusion dominance.

Abstract

It is known that electron scattering by surface polar phonons (SPPs) of the substrate reduces their mobility in supported graphene. However, there is no experimental evidence for contribution of drag of electrons by SPP to thermoelectric phenomena in graphene: graphene thermopower exhibits good agreement with Mott's law, which means that the diffusion contribution to the thermopower is dominant in a wide range of carrier densities and temperatures. Here we develop a complete theory of drag of electrons in graphene by SPP. By solving Boltzmann transport equation for electrons scattered by SPPs we derive SPP drag contribution to the thermopower in graphene. Compared to diffusion thermopower, obtained values appear to be one order of magnitude lower for various substrates. This can be explained by low occupation number of the SPPs and short mean free path of such phonons stemming from their small group velocity. We conclude that experiments on thermopower in graphene can be treated within the framework of Mott's law.