Breakdown of the interlayer coherence in twisted bilayer graphene

TL;DR

This paper demonstrates that in twisted bilayer graphene, interlayer conduction becomes incoherent and significantly suppressed, even at atomic-scale separations, due to rotational decoupling of the layers.

Contribution

It reveals that twisted bilayer graphene exhibits incoherent interlayer conduction with high resistivity, challenging the assumption of coherent charge transport in layered materials.

Findings

Interlayer resistivity exceeds that of Bernal-stacked graphite.

Resistivity shows strong temperature dependence.

External electric fields influence interlayer conduction.

Abstract

Coherent motion of the electrons in the Bloch states is one of the fundamental concepts of the charge conduction in solid state physics. In layered materials, however, such a condition often breaks down for the interlayer conduction, when the interlayer coupling is significantly reduced by e.g. large interlayer separation. We report that complete suppression of coherent conduction is realized even in an atomic length scale of layer separation in twisted bilayer graphene. The interlayer resistivity of twisted bilayer graphene is much higher than the c-axis resistivity of Bernal-stacked graphite, and exhibits strong dependence on temperature as well as on external electric fields. These results suggest that the graphene layers are significantly decoupled by rotation and incoherent conduction is a main transport channel between the layers of twisted bilayer graphene.