Conductivity of a half filled landau level

It is shown that the thermodynamic instability at the half filling of L1 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 a surface acoustic wave in the heterostructure on the surface of piezoelectric GaAs. Using the existence of two Fermi points instead of a Fermi surface suggested in the previous theoretical works, permit the explanation of the experimental results.