Berry Phase Transition in Twisted Bilayer Graphene

TL;DR

This paper reports on the observation of a Berry phase transition in twisted bilayer graphene, revealing how electronic properties can be tuned via twist angle and gating, with implications for band structure engineering.

Contribution

It presents novel magnetotransport data showing a Berry phase transition in twisted bilayer graphene, highlighting the role of layer asymmetry and magnetic field in electronic behavior.

Findings

Berry phase transition between pi and 2pi observed

Strong layer asymmetry influences electronic properties

Transition occurs at intermediate magnetic fields

Abstract

The electronic dispersion of a graphene bilayer is highly dependent on rotational mismatch between layers and can be further manipulated by electrical gating. This allows for an unprecedented control over electronic properties and opens up the possibility of flexible band structure engineering. Here we present novel magnetotransport data in a twisted bilayer, crossing the energetic border between decoupled monolayers and coupled bilayer. In addition a transition in Berry phase between pi and 2pi is observed at intermediate magnetic fields. Analysis of Fermi velocities and gate induced charge carrier densities suggests an important role of strong layer asymmetry for the observed phenomena.