Anomalous thermodiffusion of electrons in graphene

TL;DR

This paper demonstrates that electron thermodiffusion in graphene behaves counterintuitively compared to traditional models, with electrons moving toward hot regions due to their unique dispersion relation and interactions.

Contribution

It reveals the anomalous thermodiffusion behavior of Dirac electrons in graphene, contrasting it with normal diffusion in a 2DEG, highlighting the impact of material-specific dispersion relations.

Findings

Electrons in graphene move toward hot regions under a temperature gradient.

In contrast, electrons in a 2DEG move away from hot regions.

The diffusion behavior depends critically on the electron dispersion relation.

Abstract

We reveal a dramatic departure of electron thermodiffusion in solids relative to the commonly accepted picture of the ideal free-electron gas model. In particular, we show that the interaction with the lattice and impurities, combined with a strong material dependence of the electron dispersion relation, leads to counterintuitive diffusion behavior, which we identify by comparing a single-layer two-dimensional electron gas (2DEG) and graphene. When subject to a temperature gradient $\nabla T$, thermodiffusion of massless Dirac electrons in graphene exhibits an anomalous behavior with electrons moving along $\nabla T$ and accumulating in hot regions, in contrast to normal electron diffusion in a 2DEG with parabolic dispersion, where net motion against $\nabla T$ is observed, accompanied by electron depletion in hot regions. These findings have fundamentally importance for the understanding of the spatial electron dynamics in emerging material, establishing close relations with other branches of physics dealing with electron systems under nonuniform temperature conditions.