Anderson localization of electron states in graphene in different types of disorder

Abstract

Anderson localization of electron states on graphene lattice with diagonal and off-diagonal (OD) disorder in the absence of magnetic field is investigated by using the standard finite-size scaling analysis. In the presence of diagonal disorder all states are localized as predicted by the scaling theory for two-dimensional systems. In the case of OD disorder, the states at the Dirac point (E=0) are shown to be delocalized due to the specific chiral symmetry, although other states ($E\ne 0$) are still localized. In OD disorder the conductance at E=0 in an $M\times L$ rectangular system at the thermodynamical limit is calculated with the transfer-matrix technique for various values of ratio $M/L$ and different types of distribution functions of the OD elements $t_{n{n}^{\prime }}$. It is found that if all the $t_{n{n}^{\prime }}$'s are positive the conductance is independent of $L/M$ as restricted by 2 delocalized channels at E=0. If the distribution function includes the sign randomness of elements $t_{n{n}^{\prime }}$, the conductivity, rather than the conductance, becomes $L/M$ independent. The calculated value of the conductivity is around $\frac{4e^2}{h}$, in consistence with the experiments.

24 pages, 12 figures

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