The conductivity of the half filled Landau level
It is shown that the thermodynamic instability at the half filling of Ll leads to the vortex lattice formation with the electronic spectrum analogous to that of graphene with two Dirac Fermi points on Brillouin cell boundary. This result is used for the explanation of the observed current generated by SAW in the heterostructure on the surface of piezoelectric GaAs. Using the existence of two Fermi points instead Fermi surface suggested in the previous theoretical works, permit the explanation of the experimental results.