Impurity-scattering-induced carrier transport in twisted bilayer graphene

E H Hwang,S Das Sarma

doi:10.1103/physrevresearch.2.013342

E H Hwang, S Das Sarma

Open Access

https://doi.org/10.1103/physrevresearch.2.013342

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Abstract

We theoretically calculate the impurity-scattering induced resistivity of twisted bilayer graphene at low twist angles where the graphene Fermi velocity is strongly suppressed. We consider, as a function of carrier density, twist angle, and temperature, both long-ranged Coulomb scattering and short-ranged defect scattering within a Boltzmann theory relaxation time approach. For experimentally relevant disorder, impurity scattering contributes a resistivity comparable to (much larger than) the phonon scattering contribution at high (low) temperatures. Decreasing twist angle leads to larger resistivity, and in general, the resistivity increases (decreases) with increasing temperature (carrier density). Inclusion of the van Hove singularity in the theory leads to a strong increase in the resistivity at higher densities, where the chemical potential is close to a van Hove singularity, leading to an apparent density-dependent plateau type structure in the resistivity, which has been observed in recent transport experiments. We also show that the Matthissen's rule is strongly violated in twisted bilayer graphene at low twist angles.

Highlights

Electronic properties, ohmic transport properties, of twisted bilayer graphene (TBLG) are of great current interest because of the seminal experimental findings by Cao et al [1,2] at MIT that TBLG has intriguing low-temperature density- and temperature-dependent transport behavior
The effect of phonon scattering on TBLG “metallic” transport has recently been considered in the literature [7], so we focus on the effect of impurity scattering
It has been argued in Ref. [7] that the strong suppression in the TBLG Fermi velocity at low twist angles leads to a giant enhancement in the effective electron-phonon coupling, causing a large contribution to the phonon-induced temperaturedependent resistivity

Summary

INTRODUCTION

Electronic properties, ohmic transport properties, of twisted bilayer graphene (TBLG) are of great current interest because of the seminal experimental findings by Cao et al [1,2] at MIT that TBLG has intriguing low-temperature density- and temperature-dependent transport behavior Both superconducting and insulating ground states seem to exist in TBLG at various carrier densities and low twist angles [1,2,3,4]. One motivation for our considering impurity-scattering effects is the fact that disorder is known to be the most important resistive scattering source in regular (i.e., untwisted) graphene up to room temperatures because the typical electron-phonon coupling in regular graphene is weak.

THEORY AND RESULTS

INCLUSION OF VAN HOVE SINGULARITY

CONCLUSION