  The induced current density, corresponding to the massless Dirac equation in
(2+1) dimensions in a magnetic flux tube of small radius is considered. This
problem is important for graphene. In the case, when an electron can not
penetrate the region of nonzero magnetic field, this current is the odd
periodical function of the magnetic flux. If the region inside the magnetic
tube is not forbidden for penetration of electron, the induced current is not a
periodical function of the magnetic flux. However in the limit $R\to 0$, where
$R$ is the radius of magnetic flux tube, this function has the universal form
which is independent of the magnetic field distribution inside the magnetic
tube at fixed value of the magnetic flux.

Mesoscale and Nanoscale Physics