Finite Conductivity Minimum in Bilayer Graphene without Charge Inhomogeneities

TL;DR

This study demonstrates that inter-band coherence significantly influences the minimum conductivity in bilayer graphene, challenging the notion that charge inhomogeneities are necessary for finite conductivity at zero carrier density.

Contribution

It provides a numerical analysis showing the importance of inter-band coherence in graphene's transport properties, offering an alternative explanation to charge puddles.

Findings

Inter-band coherence enhances conduction near band-crossing.

Finite conductivity can occur without charge inhomogeneities.

An approximate theory captures the qualitative behavior.

Abstract

Boltzmann transport theory fails near the linear band-crossing of single-layer graphene and near the quadratic band-crossing of bilayer graphene. We report on a numerical study which assesses the role of inter-band coherence in transport when the Fermi level lies near the band-crossing energy of bilayer graphene. We find that interband coherence enhances conduction, and that it plays an essential role in graphene's minimum conductivity phenomena. This behavior is qualitatively captured by an approximate theory which treats inter-band coherence in a relaxation-time approximation. On the basis of this short-range-disorder model study, we conclude that electron-hole puddle formation is not a necessary condition for finite conductivity in graphene at zero average carrier density.