Quantum Hall criticality and localization in graphene with short-range impurities at the Dirac point.
We explore the longitudinal conductivity of graphene at the Dirac point in a strong magnetic field with two types of short-range scatterers: adatoms that mix the valleys and "scalar" impurities that do not mix them. A scattering theory for the Dirac equation is employed to express the conductance of a graphene sample as a function of impurity coordinates; an averaging over impurity positions is then performed numerically. The conductivity σ is equal to the ballistic value 4e2/πh for each disorder realization, provided the number of flux quanta considerably exceeds the number of impurities. For weaker fields, the conductivity in the presence of scalar impurities scales to the quantum-Hall critical point with σ≃4×0.4e2/h at half filling or to zero away from half filling due to the onset of Anderson localization. For adatoms, the localization behavior is also obtained at half filling due to splitting of the critical energy by intervalley scattering. Our results reveal a complex scaling flow governed by fixed points of different symmetry classes: remarkably, all key manifestations of Anderson localization and criticality in two dimensions are observed numerically in a single setup.
School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
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Gattenlöhner
School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
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Hannes
Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, 70569, Stuttgart, Germany and L. D. Landau Institute for Theoretical Physics RAS, 119334 Moscow, Russia.
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Ostrovsky
Institut für Nanotechnologie, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany and A. F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia.
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Gornyi
Institut für Nanotechnologie, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany and Institut für Theorie der kondensierten Materie and DFG Center for Functional Nanostructures, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany and Petersburg Nuclear Physics Institute, 188300 St. Petersburg, Russia.
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Mirlin
Radboud University Nijmegen, Institute for Molecules and Materials, NL-6525 AJ Nijmegen, Netherlands.
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Titov