Transport Detection of Quantum Hall Fluctuations in Graphene

TL;DR

This study investigates magnetoconductance fluctuations near the charge neutrality point in graphene, revealing mesoscopic interference effects at low fields and quantum Hall localized state effects at higher fields, indicating precursors to the quantum Hall effect.

Contribution

It identifies and distinguishes two types of conductance fluctuations in graphene near the charge neutrality point, highlighting effects of localized quantum Hall states without the presence of quantum Hall plateaus.

Findings

Mesoscopic quantum interference features at very low magnetic fields.

Additional fluctuations tracking quantum Hall sequence at fields > 0.5T.

Extraction of inhomogeneity parameters from transport data.

Abstract

Low temperature magnetoconductance measurements were made in the vicinity of the charge neutrality point. Two origins for the fluctuations were identified close to the CNP. At very low magnetic fields there exist only mesoscopic magneto-conductance quantum interference features which develop rapidly as a function of density. At slightly higher fields (> 0.5T), close to the CNP, additional fluctuations track the quantum Hall sequence expected for monolayer graphene. These additional features are attributed to effects of locally charging individual quantum Hall (QH) localized states. These effects reveal a precursor to the quantum Hall effect (QHE) since, unlike previous transport observations of QH dots charging effects, they occur in the absence of quantum Hall plateaus or Shubnikov- de Haas (SdH) oscillations. From our transport data we are able to extract parameters that characterize the inhomogeneities in our device.