Observation of the Fractional Quantum Hall Effect in Graphene

TL;DR

This paper reports the first observation of the fractional quantum Hall effect in ultraclean suspended graphene, revealing strongly correlated electron states of Dirac fermions under high magnetic fields.

Contribution

It provides experimental evidence of fractional quantum Hall states in graphene, a system previously limited by disorder, advancing understanding of correlated 2D electron systems.

Findings

Observation of fractional quantum Hall effect in graphene

Graphene becomes an insulator with a magnetic-field-tunable energy gap

Supports existence of strongly correlated Dirac fermion states

Abstract

When electrons are confined in two dimensions and subjected to strong magnetic fields, the Coulomb interactions between them become dominant and can lead to novel states of matter such as fractional quantum Hall liquids. In these liquids electrons linked to magnetic flux quanta form complex composite quasipartices, which are manifested in the quantization of the Hall conductivity as rational fractions of the conductance quantum. The recent experimental discovery of an anomalous integer quantum Hall effect in graphene has opened up a new avenue in the study of correlated 2D electronic systems, in which the interacting electron wavefunctions are those of massless chiral fermions. However, due to the prevailing disorder, graphene has thus far exhibited only weak signatures of correlated electron phenomena, despite concerted experimental efforts and intense theoretical interest. Here, we report the observation of the fractional quantum Hall effect in ultraclean suspended graphene, supporting the existence of strongly correlated electron states in the presence of a magnetic field. In addition, at low carrier density graphene becomes an insulator with an energy gap tunable by magnetic field. These newly discovered quantum states offer the opportunity to study a new state of matter of strongly correlated Dirac fermions in the presence of large magnetic fields.