Microscopic Polarization in Bilayer Graphene

TL;DR

This study uses scanning tunneling microscopy to reveal the microscopic nature of the band gap in bilayer graphene, showing its dependence on disorder and magnetic field effects, differing from previous macroscopic observations.

Contribution

It provides new microscopic insights into the bilayer graphene gap, highlighting disorder effects and interaction-induced phenomena not captured by earlier models.

Findings

The gap varies spatially with disorder potential.

The gap does not vanish at low charge densities.

A subgap opens in a magnetic field at the zero Landau level.

Abstract

Bilayer graphene has drawn significant attention due to the opening of a band gap in its low energy electronic spectrum, which offers a promising route to electronic applications. The gap can be either tunable through an external electric field or spontaneously formed through an interaction-induced symmetry breaking. Our scanning tunneling measurements reveal the microscopic nature of the bilayer gap to be very different from what is observed in previous macroscopic measurements or expected from current theoretical models. The potential difference between the layers, which is proportional to charge imbalance and determines the gap value, shows strong dependence on the disorder potential, varying spatially in both magnitude and sign on a microscopic level. Furthermore, the gap does not vanish at small charge densities. Additional interaction-induced effects are observed in a magnetic field with the opening of a subgap when the zero orbital Landau level is placed at the Fermi energy.