Electron delocalization in bilayer graphene induced by an electric field

TL;DR

This study investigates how an electric field induces a phase transition in disordered bilayer graphene, leading to electron delocalization and a divergence in localization length, resembling quantum Hall transition phenomena without magnetic fields.

Contribution

It demonstrates that electric-field-induced energy gaps in bilayer graphene can cause a localization-delocalization transition akin to quantum Hall effects, without magnetic fields.

Findings

Energy gap opening causes a phase transition with diverging localization length.

The transition resembles an integer quantum Hall transition at each valley.

Delocalization occurs in smooth disorder potentials without valley mixing.

Abstract

Electronic localization is numerically studied in disordered bilayer graphene with an electric-field induced energy gap. Bilayer graphene is a zero-gap semiconductor, in which an energy gap can be opened and controlled by an external electric field perpendicular to the layer plane. We found that, in the smooth disorder potential not mixing the states in different valleys (K and K' points), the gap opening causes a phase transition at which the electronic localization length diverges. We show that this can be interpreted as the integer quantum Hall transition at each single valley, even though the magnetic field is absent.