Quantum transport in chemically functionalized graphene at high magnetic field: defect-induced critical states and breakdown of electron-hole symmetry

arXiv:1405.3766v1Unconventional magnetotransport fingerprints in the quantum Hall regime (with applied magnetic fields from one to several tens of Tesla) in chemically functionalized graphene are reported. Upon chemical adsorption of monoatomic oxygen (from $0.5\%$ to few percents), the electron-hole symmetry of Landau levels (LLs) is broken, while a double-peaked conductivity develops at low-energy, resulting from the formation of critical states conveyed by the random network of defects-induced impurity states. Scaling analysis hints towards the existence of an additional zero-energy quantized Hall conductance plateau, which is here not connected to degeneracy lifting of LLs by sublattice symmetry breaking. This singularly contrasts with usual interpretation, and unveils a new playground for tailoring the fundamental characteristics of the quantum Hall effect.J-CC and NL acknowledge financial support from the FRS-FNRS of Belgium. This research is directly connected to the ARC on ‘Graphene Nano-electromechanics’ (no. 11/16-037) sponsored by the Communauté Française de Belgique, and funded by the Spanish Ministry of Economy and Competitiveness for funding (MAT2012-33911). This research is partly funded by the European Union Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship.Peer Reviewe