Minimal longitudinal dc conductivity of perfect bilayer graphene
Absztrakt:
We calculated the minimal longitudinal conductivity in prefect
single-layer and bilayer graphene by extending the two methods
developed for Dirac fermion gas by A. W. W. Ludwig in Phys. Rev. B 50,
7526 (1994). Using the Kubo formula which was originally applied for
spintronic systems we obtain sigma(min)(xx)=(J pi/2)e(2)/h while from
the other formula used in the above-mentioned work we find (sigma) over
bar (min)(xx)=(4J/pi)e(2)/h, where J=1 for single-layer and J=2 for
bilayer graphene. The two universal values are different although they
are numerically close to each other. Our two results are in the same
order of magnitude as that of experiments and for the single-layer case
one of our results agrees with many earlier theoretical predictions.
However, for bilayer graphene only two studies are known with
predictions for the minimal conductivity different from our calculated
values. Similarly to the single-layer case, the physical origin of the
minimal conductivity in bilayer graphene is also rooted back to the
intrinsic disorder induced by the Zitterbewegung which is related to
the trembling motion of the electron.