Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2007-02-26
Eur. Phys. J. Special Topics 148, 63 (2007)
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
11 pages, 2 EPS figures; Proceedings of Graphene Conference, MPIPKS Dresden 2006
Scientific paper
10.1140/epjst/e2007-00226-4
We study electron transport properties of a monoatomic graphite layer (graphene) with different types of disorder at half filling. We show that the transport properties of the system depend strongly on the symmetry of disorder. We find that the localization is ineffective if the randomness preserves one of the chiral symmetries of the clean Hamiltonian or does not mix valleys. We obtain the exact value of minimal conductivity $4e^2/\pi h$ in the case of chiral disorder. For long-range disorder (decoupled valleys), we derive the effective field theory. In the case of smooth random potential, it is a symplectic-class sigma model including a topological term with $\theta = \pi$. As a consequence, the system is at a quantum critical point with a universal value of the conductivity of the order of $e^2/h$. When the effective time reversal symmetry is broken, the symmetry class becomes unitary, and the conductivity acquires the value characteristic for the quantum Hall transition.
Gornyi Igor V.
Mirlin Alexander D.
Ostrovsky P. M.
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