Unconventional Sequence of Fractional Quantum Hall States in Suspended Graphene
Graphene provides a rich platform to study many-body effects, owing to its massless chiral charge carriers and the fourfold degeneracy arising from their spin and valley degrees of freedom. Graduate student Ben Feldman, Prof. Amir Yacoby, and colleagues from Max-Planck-Institut in Stuttgart used a scanning single-electron transistor to measure the local electronic compressibility of suspended graphene, and observed an unusual pattern of incompressible fractional quantum Hall states that follows the standard composite fermion sequence between filling factors ν = 0 and 1 but involves only even-numerator fractions between ν = 1 and 2. The researchers further investigated this surprising hierarchy by extracting the corresponding energy gaps as a function of the magnetic field. The sequence and relative strengths of the fractional quantum Hall states provide insight into the interplay between electronic correlations and the inherent symmetries of graphene.
Read their Report in Science 337:6099, pp. 1196-1199 | DOI: 10.1126/science.1224784