Unconventional quantum Hall effect and Berry's phase of 2pi in bilayer graphene

TL;DR

This paper reports a novel type of integer quantum Hall effect in bilayer graphene, where charge carriers with Berry's phase 2pi exhibit unique quantum dynamics and a missing zero-level plateau, contrasting with known effects.

Contribution

It introduces a third type of quantum Hall effect in bilayer graphene with Berry's phase 2pi and describes its unique quantum properties and anomalies.

Findings

Charge carriers have Berry's phase 2pi.

The zero-level Hall plateau is missing.

Metallic conductivity observed at low concentrations and high magnetic fields.

Abstract

There are known two distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems, and the other is its relativistic counterpart recently observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry's phase pi, which results in a shifted positions of Hall plateaus. Here we report a third type of the integer quantum Hall effect. Charge carriers in bilayer graphene have a parabolic energy spectrum but are chiral and exhibit Berry's phase 2pi affecting their quantum dynamics. The Landau quantization of these fermions results in plateaus in Hall conductivity at standard integer positions but the last (zero-level) plateau is missing. The zero-level anomaly is accompanied by metallic conductivity in the limit of low concentrations and high magnetic fields, in stark contrast to the conventional, insulating behavior in this regime. The revealed chiral fermions have no known analogues and present an intriguing case for quantum-mechanical studies.